Patent Publication Number: US-2023164385-A1

Title: Systems, apparatus, and methods to improve watermark detection in acoustic environments

Description:
RELATED APPLICATION 
     This patent arises from a continuation of U.S. patent application Ser. No. 17/479,918 (now U.S Pat. No. ______), which was filed on Sep. 20, 2021. U.S. patent application Ser. No. 17/479,918 is hereby incorporated herein by reference in its entirety. Priority to U.S. patent application Ser. No. 17/479,918 is hereby claimed. 
    
    
     FIELD OF THE DISCLOSURE 
     This disclosure relates generally to media watermarking and, more particularly, to systems, apparatus, and methods to improve watermark detection in acoustic environments. 
     BACKGROUND 
     Watermarks can be embedded or otherwise included in media to enable additional information to be conveyed with the media. For example, audio watermarks can be embedded and/or included in the audio data/signal portion of a media stream, file, and/or signal to convey data, such as media identification information, copyright protection information, etc., associated with the media. These watermarks enable monitoring of the distribution and/or use of media, such as by detecting watermarks present in television broadcasts, radio broadcasts, streamed multimedia, etc., to identify the particular media being presented to viewers, listeners, users, etc. The information can be valuable to advertisers, content providers, and the like. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1    is a block diagram of an example media monitoring system including an example watermark encoder to embed watermarks in media, an example watermark decoder to decode the watermarks, and an example audience measurement entity to associate access(es) of the media and demographics of users associated with the access(es). 
         FIG.  2    is a block diagram of an example implementation of the example watermark encoder of  FIG.  1   . 
         FIG.  3    is a block diagram of an example implementation of the example watermark decoder of  FIG.  1   . 
         FIG.  4    is a block diagram of an example implementation of the example audience measurement entity of  FIG.  1   . 
         FIG.  5    depicts example watermarks in media at different example frequency layers. 
         FIG.  6    depicts an example dense single-layer watermark and an example dense multilayer watermark. 
         FIG.  7    depicts a first example sparse multilayer watermark and a second example sparse multilayer watermark. 
         FIG.  8    depicts an example single-layer watermark including example symbols corresponding to an example media identifier and an example timestamp. 
         FIG.  9    depicts an example multilayer watermark including example symbols corresponding to an example media identifier, an example timestamp, and example error-checking data. 
         FIG.  10    is a flowchart representative of example machine readable instructions and/or example operations that may be executed by example processor circuitry to implement the example watermark encoder of  FIGS.  1  and/or  2   , the example watermark decoder of  FIGS.  1  and/or  3   , and/or the example audience measurement entity of  FIGS.  1  and/or  4    to associate access of media and demographics of user(s) associated with device(s). 
         FIG.  11    is a flowchart representative of example machine readable instructions and/or example operations that may be executed by example processor circuitry to implement the example watermark encoder of  FIGS.  1  and/or  2    to encode media with sparse watermarks to indicate the media is accessed within a time period after publishing of the media. 
         FIG.  12    is a flowchart representative of example machine readable instructions and/or example operations that may be executed by example processor circuitry to implement the example watermark encoder of  FIGS.  1  and/or  2   , the example watermark decoder of  FIGS.  1  and/or  3   , and/or the example audience measurement entity of  FIGS.  1  and/or  4    to associate demographics of user(s) with accessed media based on at least one of media identifiers or timestamps. 
         FIG.  13    is a flowchart representative of example machine readable instructions and/or example operations that may be executed by example processor circuitry to implement the example watermark encoder of  FIGS.  1  and/or  2    to encode media with multilayer watermarks to convey at least one of media identifiers or timestamps. 
         FIG.  14    is a block diagram of an example processing platform including processor circuitry structured to execute the example machine readable instructions and/or the example operations of  FIGS.  10 ,  11 ,  12   , and/or  13  to implement the example watermark encoder of  FIGS.  1  and/or  2   . 
         FIG.  15    is a block diagram of an example processing platform including processor circuitry structured to execute the example machine readable instructions and/or the example operations of  FIGS.  10  and/or  12    to implement the example watermark decoder of  FIGS.  1  and/or  3   . 
         FIG.  16    is a block diagram of an example processing platform including processor circuitry structured to execute the example machine readable instructions and/or the example operations of  FIGS.  10  and/or  12    to implement the example audience measurement entity of  FIGS.  1  and/or  4   . 
         FIG.  17    is a block diagram of an example implementation of the processor circuitry of  FIGS.  14 ,  15   , and/or  16 . 
         FIG.  18    is a block diagram of another example implementation of the processor circuitry of  FIGS.  14 ,  15   , and/or  16 . 
         FIG.  19    is a block diagram of an example software distribution platform to distribute software to client devices associated with end users and/or consumers, retailers, and/or original equipment manufacturers (OEMs). 
     
    
    
     The figures are not to scale. In general, the same reference numbers will be used throughout the drawing(s) and accompanying written description to refer to the same or like parts. 
     DETAILED DESCRIPTION 
     Unless specifically stated otherwise, descriptors such as “first,” “second,” “third,” etc., are used herein without imputing or otherwise indicating any meaning of priority, physical order, arrangement in a list, and/or ordering in any way, but are merely used as labels and/or arbitrary names to distinguish elements for ease of understanding the disclosed examples. In some examples, the descriptor “first” may be used to refer to an element in the detailed description, while the same element may be referred to in a claim with a different descriptor such as “second” or “third.” In such instances, it should be understood that such descriptors are used merely for identifying those elements distinctly that might, for example, otherwise share a same name. As used herein “substantially real time” and “substantially simultaneously” refer to occurrences in a near instantaneous manner recognizing there may be real world delays for computing time, transmission, etc. Thus, unless otherwise specified, “substantially real time” and “substantially simultaneously” refer to real time +/−1 second. As used herein, the phrase “in communication,” including variations thereof, encompasses direct communication and/or indirect communication through one or more intermediary components, and does not require direct physical (e.g., wired) communication and/or constant communication, but rather additionally includes selective communication at periodic intervals, scheduled intervals, aperiodic intervals, and/or one-time events. 
     As used herein, “processor circuitry” is defined to include (i) one or more special purpose electrical circuits structured to perform specific operation(s) and including one or more semiconductor-based logic devices (e.g., electrical hardware implemented by one or more transistors), and/or (ii) one or more general purpose semiconductor-based electrical circuits programmed with instructions to perform specific operations and including one or more semiconductor-based logic devices (e.g., electrical hardware implemented by one or more transistors). Examples of processor circuitry include programmed microprocessors, Field Programmable Gate Arrays (FPGAs) that may instantiate instructions, Central Processor Units (CPUs), Graphics Processor Units (GPUs), Digital Signal Processors (DSPs), XPUs, or microcontrollers and integrated circuits such as Application Specific Integrated Circuits (ASICs). For example, an XPU may be implemented by a heterogeneous computing system including multiple types of processor circuitry (e.g., one or more FPGAs, one or more CPUs, one or more GPUs, one or more DSPs, etc., and/or a combination thereof) and application programming interface(s) (API(s)) that may assign computing task(s) to whichever one(s) of the multiple types of the processing circuitry is/are best suited to execute the computing task(s). 
     Systems, apparatus, and methods to improve watermark detection in acoustic environments are disclosed. Watermarks can be embedded or otherwise included in media to enable additional information to be conveyed with the media. The watermarks enable monitoring of the distribution and/or use of media by identifying the particular media being presented to viewers, listeners, users, etc. The information can be valuable to advertisers, content providers, and the like. Some known media monitoring systems employing watermarks typically include watermark encoders that encode watermarks that are unique for individual media content files. However, depending on the encoding methodology employed, the ability to detect such watermarks in acoustic environments, such as noisy, loud volume, etc., type environments, may be substantially or entirely diminished. 
     Some watermark encoding techniques are described in U.S. patent application No. 13/955,245 (U.S. Pat. No. 9,711,152), entitled SYSTEMS, APPARATUS AND METHODS FOR ENCODING/DECODING PERSISTENT UNIVERSAL MEDIA CODES TO ENCODED AUDIO, U.S. patent application Ser. No. 13/955,438 (U.S. Publication No. 2015/0039321), entitled APPARATUS, SYSTEM AND METHOD FOR READING CODES FROM DIGITAL AUDIO ON A PROCESSING DEVICE, U.S. patent application Ser. No. 14/023,221 (U.S. Publication No. 2015/0039322), entitled APPARATUS, SYSTEM AND METHOD FOR MERGING CODE LAYERS FOR AUDIO ENCODING AND DECODING, U.S. patent application Ser. No. 14/587,995 (U.S. Pat. No. 9,418,395), entitled POWER EFFICIENT DETECTION OF WATERMARKS IN MEDIA SIGNALS, and U.S. patent application Ser. No. 15/994,383 (U.S. Pat. No. 10,694,243), entitled METHODS AND APPARATUS TO IDENTIFY MEDIA BASED ON WATERMARKS ACROSS DIFFERENT AUDIO STREAMS AND/OR DIFFERENT WATERMARKING TECHNIQUES. 
     Examples disclosed herein can improve watermark detection in media published on on-demand platforms. Unlike a linear program that airs on a set schedule (e.g., a program published over-the-air, or via cable, satellite, network, etc., on a broadcast or distribution schedule), some on-demand platforms have no set airing schedule. Instead, viewers may select media from a menu of media and watch and/or otherwise access the media when convenient for the viewers. Some on-demand platforms publish media for access by viewers within a specific time period after an initial publishing of the media and/or after an availability of the media on a media platform (e.g., a streaming media platform). In some examples, such on-demand platforms may implement recently telecast video-on demand (RTVOD) platforms or media providers. In some examples, RTVOD platforms may publish media on a first day and may make the media available for on-demand media presentation within a first time period (e.g., within three days after initial publishing), a second time period (e.g., within seven days of initial publishing), etc., after the initial publishing on the first day. In some such examples, the RTVOD platforms may be media platforms (e.g., on-demand media platforms, streaming media platforms, etc.) maintained by streaming media providers such as Netflix™, Hulu™, Prime Video™, HBO MAX™, Showtime™, etc. 
     An audience measurement entity (AME), such as the Nielsen Company (US), LLC, may facilitate the encoding of watermarks in RTVOD media in an effort to understand the demographic compositions of viewing audiences of such media within the first time period, the second time period, etc., after the initial publishing on the first day. For example, a media presentation device may access RTVOD media that is embedded with watermarks, and a meter may detect the watermarks embedded in audio of the RTVOD media in response to the media presentation device accessing and/or presenting the RTVOD media. In some such examples, in response to the meter detecting the watermarks, the meter may provide an indication to the AME that the media presentation device accessed and/or presented the RTVOD media. However, the detection of watermarks embedded in RTVOD media may be substantially or completely diminished when the RTVOD media is accessed in acoustic environments, such as noisy, loud volume, etc., type environments, which may include bars, restaurants, outdoor environments, etc. 
     Some on-demand platforms publish media that did not air within the past seven days on linear programming distribution in the same exact form, or did not air on linear programming distribution at all. In some examples, such on-demand platforms may implement library video-on demand (VOD) platforms or media providers. Examples of some such library VOD platforms may include libraries of programs that are made for on-demand presentation, movies that are no longer showing in theatres, prior seasons of network or cable programs, current-season telecasts with changed commercial content, etc. AMEs desire to understand the demographic compositions of viewing audiences of such media. 
     An AME may facilitate the encoding of watermarks in library VOD media in an effort to understand the demographic compositions of viewing audiences of such media. For example, a media presentation device may access/present library VOD media embedded with watermarks, and a meter may identify the watermarks embedded in audio of the library VOD media in response to the media presentation device accessing/presenting the library VOD media. In some such examples, the meter may provide an indication to the audience measurement entity that the media presentation device accessed/presented the library VOD media, with the meter providing the indication in response to the meter identifying the watermarks. However, the detection of watermarks embedded in library VOD media may be substantially or completely diminished when the library VOD media is accessed in acoustic environments, such as noisy, loud volume, etc., type environments. 
     Examples disclosed herein can improve watermark detection in media accessed in acoustic environments by utilizing multilayer watermarks. In some disclosed examples, a watermark encoder may generate sparse multilayer watermarks by (i) inserting watermark symbol(s) at one or more first symbol positions of a first watermark layer while leaving one or more second symbol positions of the first watermark layer empty and/or otherwise not filled with watermark symbol(s), and (ii) inserting watermark symbol(s) at one or more second symbol positions of a second watermark layer while leaving one or more second symbol positions of the second watermark layer empty and/or otherwise not filled with watermark symbol(s). For example, a symbol position may be empty when the symbol position does not contain a symbol. In some such examples, a symbol may not be encoded, embedded, etc., at the empty symbol position. In some disclosed examples, the watermark encoder may select one(s) of the watermark symbols to convey a state (e.g., a media state) of accessed media. For example, the state may be a first state (e.g., a first media state) that corresponds to media being accessed and/or presented within a first time period after an initial publishing of the media. In some such examples, the first state may implement a C3 media state that indicates that RTVOD media is being accessed/presented within three days of the initial publishing. In some examples, the state may be a second state (e.g., a second media state) that corresponds to the media being accessed and/or presented within a second time period after the initial publishing. In some such examples, the first state may implement a C7 media state that indicates that RTVOD media is being accessed/presented within seven days of the initial publishing. In some examples, the watermark encoder may embed RTVOD media with sparse multilayer watermarks to increase a likelihood of detection of the state of the media. For example, the watermark encoder may utilize watermark layers associated with frequencies that have improved detection capability to increase a likelihood of detecting the sparse multilayer watermarks. 
     In some disclosed examples, a watermark encoder may generate a multilayer watermark that conveys timestamps (e.g., timestamp or other time data associated with media presentation) using frequencies that have improved detection capability to increase a likelihood of detecting such a watermark. In some disclosed examples, the watermark encoder may convert (i) a first timestamp in a first format based on a number of seconds at which a watermark is to be inserted into media into (ii) a second timestamp in a second format based on a number of minutes at which the watermark is to be inserted into the media. In some disclosed examples, the watermark encoder may determine a first bit sequence that may be inserted into a first watermark layer of the multilayer watermark and a second bit sequence that may be inserted into a second watermark layer of the multilayer watermark. In some disclosed examples, the watermark encoder may insert one or more error checking or parity bits into at least one of the first bit sequence or the second bit sequence for improved watermark detection. Advantageously, the example watermark encoder may distribute the timestamp data amongst different layers of a multilayer watermark to increase a likelihood of detecting the multilayer watermark in acoustic environments. For example, a watermark decoder may extract the first bit sequence from the first watermark layer and the second bit sequence from the second watermark layer and assemble the timestamp using the first bit sequence and the second bit sequence. 
       FIG.  1    is a block diagram of an example media monitoring system  100  including an example media provider  102 , an example audience measurement entity (AME)  104 , an example watermark encoder  106 , a first example network  108 , a second example network  110 , an example media presentation device  112 , a first example panelist device  114 , an example panelist  116 , and a second example panelist device  118 . In the illustrated example, the first panelist device  114  is an Internet-enabled smartphone. The first panelist device  114  of the illustrated example includes a first example meter  120 , which may include and/or otherwise implement at least one of first example input device circuitry  122  or a first example watermark decoder  124 . In the illustrated example, the panelist  116  is wearing the second panelist device  118 , which includes a second example meter  126 . For example, the second panelist device  118  may be a wrist-watch type device, a smartwatch, a fitness tracker, etc. The second meter  126  may include and/or otherwise implement at least one of a second example watermark decoder  127  or second example input device circuitry  128 . In some examples, the first input device circuitry  122  and/or the second input device circuitry  128  may be implemented by, for example, an audio sensor, a microphone, etc., or any other type of sensor and/or circuitry that may detect audio (e.g., audio data, audio signals, audio waveforms, etc.). 
     The media monitoring system  100  of the illustrated example supports monitoring of media presented at one or more monitored sites, such as an example monitored site  130 . The monitored site  130  includes the media presentation device  112 . Although the example of  FIG.  1    illustrates one monitored site  130  and one media presentation device  112 , improved watermark detection in acoustic environments as disclosed herein can be implemented in media monitoring systems  100  supporting any number of monitored sites  130  having any number of media presentation devices  112 . 
     The media provider  102  of the illustrated example corresponds to any one or more media providers capable of providing media for presentation via the media presentation device  112 . The media provided by the media provider  102  can include any type(s) of media, such as audio, video, multimedia, etc. Additionally, the media can correspond to live media, streaming media, broadcast media, stored media, on-demand content, etc. 
     In some examples, the media provider  102  of the illustrated example may be implemented by one or more servers providing streaming media (e.g., web pages, audio, videos, images, etc.). For example, the media provider  102  may be implemented by any provider(s) of media such as a digital broadcast provider (cable television service, fiber-optic television service, etc.) and/or an on-demand digital media provider (e.g., Internet streaming video and/or audio services such as Netflix®, YouTube®, Hulu®, Pandora®, Last.fm®, HBO MAX™, etc.) and/or any other provider of streaming media services. In some other examples, the media provider  102  is a host for web site(s). Additionally or alternatively, the media provider  102  may not be on the Internet. For example, the media provider  102  may be on a private and/or semi-private network (e.g., a LAN, a virtual private network, etc.) to which the media presentation device  112  connects. 
     The AME  104  of the illustrated example may be implemented by one or more servers that collect and process media monitoring information from the first meter  120  and/or the second meter  126  to generate exposure metrics, identify demographic trends, etc., related to presented media. The media monitoring information may also be correlated or processed with factors such as geodemographic data (e.g., a geographic location of the media exposure measurement location, age(s) of the panelist(s)  116  associated with the monitored site  130 , an income level of a panelist  116 , etc.). Media monitoring information may be useful to advertisers to determine which media is popular or trending among users, identify geodemographic trends with respect to presentation of media, identify market opportunities, and/or otherwise evaluate their own and/or their competitors&#39; media. 
     In the illustrated example, the media provider  102  may provide media to be embedded with watermarks to at least one of the AME  104  or the watermark encoder  106 . In some examples, the AME  104  may generate a source identifier (SID) that uniquely identifies the media provider  102 . The AME  104  may provide the SID to the media provider  102 . The AME  104  may generate timestamps of the media, which may be referred to as time-in content (TIC) indicators, markers, data, etc. In some examples, the media provider  102  may generate the media timestamps and provide the media timestamps to at least one of the AME  104  or the watermark encoder  106 . In some examples, the watermark encoder  106  may generate the media timestamps. 
     In the illustrated example, the watermark encoder  106  embeds watermarks in media generated by the media provider  102  that can be decoded by the watermark decoder  124 ,  127  when the media is presented by the media presentation device  112 . For example, the media provider  102  and/or the AME  104  may provide at least one of the media to be encoded (e.g., embedded with watermarks), a media identifier that identifies the media, the SID corresponding to the media provider  102 , and/or timestamps (e.g., TIC markers) to the watermark encoder  106 . In some examples, the watermark encoder  106  may generate the timestamps while sequentially embedding watermarks in the media obtained from the media provider  102  and/or the AME  104 . The watermark encoder  106  may generate watermarks that include at least one of the media identifier, the SID, and/or the timestamps. The watermark encoder  106  may encode the media by embedding the watermarks into the media. For example, the watermark encoder  106  may embed the at least one of the media identifier, the SID, and/or the timestamps, or portion(s) thereof, across one or more layers of multilayered watermarks associated with one or more frequencies (e.g., acoustic frequencies) that may be detected by the watermark decoder  124 ,  127 . Advantageously, the watermark encoder  106  may generate the multilayered watermarks by inserting portion(s) of data to be embedded, such as the media identifier, the SID, and/or the timestamps, at one or more symbol positions of one or more layers of the multilayered watermark. The watermark encoder  106  may provide, deliver, and/or otherwise transmit the encoded media to the media presentation device  112  via the first network  108 . Alternatively, the watermark encoder  106  may provide the encoded media to the media provider  102 . In such examples, the media provider  102  may provide the encoded media to the media presentation device  112  via the first network  108 . 
     The first network  108  and/or the second network  110  of the illustrated example is/are the Internet. However, the first network  108  and/or the second network  110  may be implemented using any suitable wired and/or wireless network(s) including, for example, one or more data buses, one or more Local Area Networks (LANs), one or more wireless LANs, one or more cellular networks, one or more private networks, one or more public networks, etc. The first network  108  enables the media provider  102  and/or the watermark encoder  106  to be in communication with the media presentation device  112 . The second network  110  enables the AME  104  to be in communication with at least one of the first meter  120  or the second meter  126 . 
     The media monitoring system  100  of the illustrated example includes the first meter  120  and/or the second meter  126  to monitor media presented by the media presentation device  112 . In some examples, the first meter  120  and/or the second meter  126  may be referred to as a media device meter, a site meter, a site unit, a home unit, a portable device, a people meter, a wearable meter, etc. In the illustrated example, the media monitored by the first meter  120  and/or the second meter  126  can correspond to any type of media presentable by the media presentation device  112 . For example, monitored media can correspond to media content, such a television programs, radio programs, movies, Internet video, recently telecast video on demand (RTVOD), library video-on-demand (VOD), etc., as well as commercials, advertisements, etc. 
     In the illustrated example, the first meter  120  and/or the second meter  126  determine metering data that may identify and/or be used to identify media presented by the media presentation device  112  (and, thus, infer media exposure) at the monitored site  130 . In some examples, the first meter  120  and/or the second meter  126  may store and report such metering data via the second network  110  to the AME  104 . The AME  104  performs any appropriate post-processing of the metering data to, for example, determine audience ratings information, identify demographics of users that accessed the media, identify targeted advertising to be provided to the monitored site  130 , etc. 
     In the illustrated example, the media presentation device  112  monitored by the first meter  120  and/or the second meter  126  can correspond to any type of audio, video and/or multimedia presentation device capable of presenting media audibly and/or visually. In this example, the media presentation device  112  is a television (e.g., a smart television, an Internet-enabled television, etc.). For example, the media presentation device  112  can correspond to a television and/or display device that supports the National Television Standards Committee (NTSC) standard, the Phase Alternating Line (PAL) standard, the Systeme Electronique pour Couleur avec Mémoire (SECAM) standard, a standard developed by the Advanced Television Systems Committee (ATSC), such as high definition television (HDTV), a standard developed by the Digital Video Broadcasting (DVB) Project, etc. As other examples, the media presentation device  112  can correspond to a multimedia computer system, a personal digital assistant, a cellular/mobile smartphone, a radio, a tablet computer, etc. 
     In the media monitoring system  100  of the illustrated example, the first meter  120 , the second meter  126 , and the AME  104  cooperate to perform media monitoring based on detecting media watermarks. Moreover, the first meter  120  and/or the second meter  126  detect media multilayer watermarks as disclosed herein for improved detection in acoustic environments. Examples of watermarks include identification codes, ancillary codes, etc., that may be transmitted within media signals. For example, identification codes can be transmitted as watermarked data embedded or otherwise included with media (e.g., inserted into the audio, video, or metadata stream of media) to uniquely identify broadcasters and/or media (e.g., content or advertisements). Watermarks can additionally or alternatively be used to carry other types of data, such as copyright protection information, secondary data (e.g., such as one or more hyperlinks pointing to secondary media retrievable via the Internet and associated with the primary media carrying the watermark), commands to control one or more devices, etc. Watermarks are typically extracted using a decoding operation, which may be implemented by the watermark decoder  124 ,  127  in this example. 
     In contrast, signatures are a representation of some characteristic of the media signal (e.g., a characteristic of the frequency spectrum of the signal). Signatures can be thought of as fingerprints. They are typically not dependent upon insertion of data in the media, but instead preferably reflect an inherent characteristic of the media and/or the signal transporting the media. Systems to utilize codes and/or signatures for audience measurement are long known. See, for example, U.S. Pat. No. 5,481,294 to Thomas et al., which is hereby incorporated by reference in its entirety. 
     In the illustrated example, the first meter  120  and the second meter  126  are implemented by portable devices (e.g., an Internet-enabled handset, a handheld device, a wearable device, a smartwatch, etc.) including the first input device circuitry  122 , the first watermark decoder  124 , the second watermark decoder  127 , and/or the second input device circuitry  128 . For example, the first meter  120  of the illustrated example may be implemented by an Internet-enabled handset, smartphone, etc. The second meter  126  of the illustrated example may be implemented by a wearable device (e.g., wrist-watch type device, a smartwatch, a fitness tracker, etc.). 
     In the illustrated example, the first input device circuitry  122  and/or the second input device circuitry  128  may capture audio generated by example audio devices  132  (e.g., speaker(s) of the media presentation device  112 ). The first input device circuitry  122  and/or the second input device circuitry  128  may provide the audio to a respective one of the watermark decoders  124 ,  127 . The watermark decoders  124 ,  127  are configured to detect watermark(s) in media signal(s) (e.g., audio) output from a monitored media device, such as the media presentation device  112 . 
     In some examples, the first meter  120  and/or the second meter  126  correspond to special purpose portable device(s) constructed to implement a respective one of the watermark decoders  124 ,  127 . For example, the first meter  120  may be an application (e.g., a software and/or firmware application) that can be executed by the first panelist device  114  to extract watermarks from audio generated in response to an access of media by the media presentation device  112 . In some such examples, the first meter  120  may utilize the first watermark decoder  124  to extract the watermarks. In some examples, the second meter  126  may be an application (e.g., a software and/or firmware application) that can be executed by the second panelist device  118  to extract watermarks from audio output from the audio devices  132 . In some such examples, the second meter  126  may utilize the second watermark decoder  127  to extract the watermarks. 
     In some examples, the first meter  120  and/or the second meter  126  can be implemented by any portable device capable of being adapted (via hardware changes, software changes, firmware changes, etc., or any combination thereof) to implement a respective one of the watermark decoders  124 ,  127 . As such, the first meter  120  and/or the second meter  126  can be implemented by a smartphone, a tablet computer, a handheld device, a wrist-watch type device, other wearable devices, a special purpose device, etc. In some examples, the first meter  120  and/or the second meter  126  can be implemented by a portable device that, although portable, is intended to be relatively stationary. Furthermore, in some examples, the first meter  120  and/or the second meter  126  can be implemented by or otherwise included in the media presentation device  112 , such as when the media presentation device  112  corresponds to a portable device (e.g., a smartphone, a tablet computer, a handheld device, etc.) capable of presenting media. (This latter implementation can be especially useful in example scenarios in which a media monitoring application is executed on the media presentation device  112  itself, but the media presentation device  112  prevents, e.g., via digital rights management or other techniques, third-party applications, such as the media monitoring application, from accessing protected media data stored on the media presentation device  112 .). 
     The terms “media data” and “media” as used herein mean data which is widely accessible, whether over-the-air, or via cable, satellite, network, internetwork (including the Internet), print, displayed, distributed on storage media, or by any other means or technique that is humanly perceptible, without regard to the form or content of such data, and including but not limited to audio, video, audio/video, text, images, animations, databases, broadcasts, displays (including but not limited to video displays, posters and billboards), signs, signals, web pages, print media and streaming media data. 
       FIG.  2    is a block diagram of an example implementation of the example watermark encoder  106  of  FIG.  1    to encode media with multilayered watermarks to improve watermark detection in acoustic environments. The watermark encoder  106  of  FIG.  2    may be instantiated by processor circuitry such as a central processing unit executing instructions. Additionally or alternatively, the watermark encoder  106  of  FIG.  2    may be instantiated by an ASIC or an FPGA structured to perform operations corresponding to the instructions. 
     The watermark encoder  106  of the illustrated example of  FIG.  2    includes example interface circuitry  210 , example media identification generator circuitry  220 , example source identification (SID) generator circuitry  230 , example timestamp generator circuitry  240 , example dense watermark embedder circuitry  250 , example sparse watermark embedder circuitry  260 , an example datastore  270 , and an example bus  280 . In this example, the datastore  270  includes example media  272 , example identifiers  274 , example timestamps  276 , and example watermarks  278 . The interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , and/or the datastore  270  is/are in communication with one(s) of each other by the bus  280 . For example, the bus  280  may be implemented by at least one of an Inter-Integrated Circuit (I2C) bus, a Serial Peripheral Interface (SPI) bus, or a Peripheral Component Interconnect (PCI) bus. Additionally or alternatively, the bus  280  may implement any other type of computing or electrical bus. 
     The watermark encoder  106  includes the interface circuitry  210  to receive and/or transmit data. In some examples, the interface circuitry  210  receives and/or otherwise obtains at least one of the media  272 , the identifiers  274 , or the timestamps  276  from at least one of the media provider  102  or the AME  104  of  FIG.  1   . For example, the interface circuitry  210  may obtain the media  272  for encoding. In some examples, the interface circuitry  210  may implement a web server that receives data from the media provider  102  and/or the AME  104 . In some examples, the interface circuitry  210  may implement a web server that transmits data to the media provider  102 , the AME  104 , and/or the media presentation device  112 . In some examples, the interface circuitry  210  may receive and/or transmit data formatted as an HTTP message. However, any other message format and/or protocol may additionally or alternatively be used such as, for example, a file transfer protocol (FTP), a simple message transfer protocol (SMTP), an HTTP secure (HTTPS) protocol, etc. In some examples, the interface circuitry  210  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a universal serial bus (USB) interface, a Bluetooth® interface, a near field communication (NFC) interface, a Peripheral Component Interconnect (PCI) interface, and/or a Peripheral Component Interconnect Express (PCIe) interface. 
     The watermark encoder  106  includes the media identification generator circuitry  220  to generate a media identifier that identifies the media  272 . In some such examples, the media identification generator circuitry  220  may generate the media identifier to be inserted into a watermark, such as a multilayered watermark as disclosed herein. In some examples, the media identification generator circuitry  220  generates the media identifier based on the media  272  (e.g., a title, a duration, etc., or any other data associated with the media  272 ). In some examples, the media identification generator circuitry  220  determines whether the media  272  is scheduled and/or otherwise intended to be accessed by device(s) (e.g., the media presentation device  112  of  FIG.  1   ) after publishing of the media  272  by the media provider  102  of  FIG.  1   . For example, the media identification generator circuitry  220  may determine when the media  272  is to be accessed by device(s) based on data included with a request to encode the media  272  from at least one of the media provider  102  or the AME  104 . In some such examples, the request may include metadata, a command or instruction, or any other data to indicate whether the media  272  is scheduled to be accessed as a linear program, as an RTVOD program, a library VOD program, etc. In some examples, the media identification generator circuitry  220  may identify the media  272  as a linear program in response to a determination that the media  272  is not to be accessed by the media presentation device  112  after an initial publishing of the media  272  (e.g., the media  272  is to be accessed by the media presentation device  112  concurrently with the publishing of the media  272 ). 
     In some examples, the media identification generator circuitry  220  determines whether the media  272  is scheduled and/or otherwise intended to be accessed by device(s) after a premiere or initial publishing of the media  272 . For example, the media identification generator circuitry  220  can determine whether the media  272  is scheduled, slated, planned, programmed, tagged, identified, etc., to be accessed by device(s) within a first time period (e.g., within three days, within four days, etc.) after the publishing of the media  272 . In some examples, the media identification generator circuitry  220  determines whether the media  272  is scheduled to be accessed by device(s) within a second time period (e.g., within seven days, within eighth days, etc.) after the publishing of the media  272 . In some examples, the media identification generator circuitry  220  determines whether a media file (e.g., the media  272 ) has completed an encoding process. 
     The watermark encoder  106  includes the SID generator circuitry  230  to generate a SID that identifies a provider (e.g., a media provider), a generator, a distributor, and/or otherwise publisher of the media  272 . For example, the SID generator circuitry  230  may generate a SID that identifies the media provider  102 . In some such examples, the SID generator circuitry  230  may generate the SID to be inserted into a watermark, such as a multilayered watermark as disclosed herein. 
     The watermark encoder  106  includes the timestamp generator circuitry  240  to generate timestamps. In some examples, the timestamp generator circuitry  240  may generate a timestamp to be inserted into a watermark, such as a multilayered watermark as disclosed herein. In some examples, the timestamp generator circuitry  240  generates the timestamp to be distributed across one or more layers of a multilayered watermark. In some examples, the timestamp generator circuitry  240  may generate one or more error check or parity bits to be associated with the timestamp. For example, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may encode the timestamp and one or more parity bits into one or more layers of a multilayer watermark. 
     The watermark encoder  106  includes the dense watermark embedder circuitry  250  to generate a watermark in which an entirety or substantial quantity of symbol positions of the watermark are filled with symbols (e.g., watermark symbols, data symbols, audio encoding symbols, etc.). For example, the dense watermark embedder circuitry  250  may generate a dense watermark that has eight symbol positions by inserting a symbol at every one of the eight symbol positions. In some examples, the dense watermark embedder circuitry  250  may encode the media  272  with dense watermarks to indicate that the media  272  is accessed during a premiere or initial publishing of the media  272 . 
     In some examples, the dense watermark embedder circuitry  250  may encode the media  272  with single layer watermarks to convey at least one of media identifiers or timestamps. In some examples, the dense watermark embedder circuitry  250  may encode the media  272  with multilayer watermarks to convey at least one of media identifiers or timestamps. 
     The watermark encoder  106  includes the sparse watermark embedder circuitry  260  to generate a watermark in which a substantial portion of symbol positions of a watermark is empty and/or otherwise not filled with a symbol. For example, the sparse watermark embedder circuitry  260  may generate a sparse watermark that has eight symbol positions by inserting a symbol at one or two of the eight symbol positions. In some examples, the sparse watermark embedder circuitry  260  may encode the media  272  with sparse watermarks to indicate that the media  272  is accessed after a premiere or initial publishing of the media  272 . For example, the sparse watermark embedder circuitry  260  may encode the media  272  with sparse watermarks to indicate that the media  272  is accessed within three days, within seven days, etc., after the premiere of the media  272  on a platform (e.g., a media platform, a media provider platform, etc.). 
     In some examples, the sparse watermark embedder circuitry  260  may encode the media  272  with sparse single layer watermarks to convey at least one of media identifiers or timestamps. In some examples, the sparse watermark embedder circuitry  260  may encode the media  272  with sparse multilayer watermarks to convey at least one of media identifiers or timestamps. For example, the sparse watermark embedder circuitry  260  may select a first symbol to be inserted at a first symbol position on a first encoding layer of a multilayered watermark. In some such examples, the sparse watermark embedder circuitry  260  may select that one or more of the remaining symbol positions on the first encoding layer is/are to remain empty and/or otherwise not include a symbol. In some examples, the sparse watermark embedder circuitry  260  may select a second symbol to be inserted at a second symbol position on a second encoding layer of the multilayered watermark. In some such examples, the sparse watermark embedder circuitry  260  may select that one or more of the remaining symbol positions on the second encoding layer is/are to remain empty and/or otherwise not include a symbol (e.g., a symbol is not encoded, embedded, etc., at the empty symbol positions). The sparse watermark embedder circuitry  260  may encode the first symbol in a media file (e.g., the media  272 ) at the first symbol position on the first encoding layer. The sparse watermark embedder circuitry  260  may encode the second symbol in the media file at the second symbol position on the second encoding layer. In some examples, the sparse watermark embedder circuitry  260  may select the first symbol, the second symbol, and the placement(s) of the first and second symbols to indicate that the media  272  is to be accessed within a first time period, a second time period, etc., after the premiere of the media  272 . 
     The watermark encoder  106  of the illustrated example includes the datastore  270  to record data (e.g., the media  272 , the identifiers  274 , the timestamps  276 , the watermarks  278 , etc.). For example, the datastore  270  may store the media  272 , which may include unencoded and/or encoded media. In some such examples, the datastore  270  may record the media  272  obtained from at least one of the media provider  102  or the AME  104  of  FIG.  1   . The datastore  270  may store the identifiers  274 , which may include media identifiers generated by the media identification generator circuitry  220 , SIDs generated by the SID generator circuitry  230 , etc. The datastore  270  may store the timestamps  276  generated by the timestamp generator circuitry  240 . The datastore  270  may store the watermarks  278  generated by at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260 . 
     The datastore  270  may be implemented by a volatile memory (e.g., a Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAIVIBUS Dynamic Random Access Memory (RDRAM), etc.) and/or a non-volatile memory (e.g., flash memory). The datastore  270  may additionally or alternatively be implemented by one or more double data rate (DDR) memories, such as DDR, DDR2, DDR3, DDR4, mobile DDR (mDDR), etc. The datastore  270  may additionally or alternatively be implemented by one or more mass storage devices such as hard disk drive(s) (HDD(s)), compact disk (CD) drive(s), digital versatile disk (DVD) drive(s), solid-state disk (SSD) drive(s), etc. While in the illustrated example the datastore  270  is illustrated as a single datastore, the datastore  270  may be implemented by any number and/or type(s) of datastores. Furthermore, the data stored in the datastore  270  may be in any data format such as, for example, binary data, comma delimited data, tab delimited data, structured query language (SQL) structures, etc. In some examples, the datastore  270  implements one or more databases. The term “database” as used herein means an organized body of related data, regardless of the manner in which the data or the organized body thereof is represented. For example, the organized body of related data may be in the form of one or more of a table, a map, a grid, a packet, a datagram, a frame, a file, an e-mail, a message, a document, a report, a list or in any other form. 
     In some examples, the watermark encoder  106  includes means for encoding a symbol in a media file. For example, the means for encoding may be implemented by at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , or the datastore  270 . In some examples, the at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , or the datastore  270  may be instantiated by processor circuitry such as the example processor circuitry  1412  of  FIG.  14   . For instance, the at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , or the datastore  270  may be instantiated by the example general purpose processor circuitry  1700  of  FIG.  17    executing machine executable instructions such as that implemented by at least blocks  1002 ,  1004 ,  1006 ,  1008  of  FIG.  10   , blocks  1102 ,  1104 ,  1106 ,  1108 ,  1110 ,  1112 ,  1114 ,  1116 ,  1118 ,  1120 ,  1122  of  FIG.  11   , blocks  1202 ,  1204 ,  1206 ,  1208  of  FIG.  12   , and/or blocks  1302 ,  1304 ,  1306 ,  1308 ,  1310 ,  1312 ,  1314 ,  1316 ,  1318  of  FIG.  13   . In some examples, the at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , or the datastore  270  may be instantiated by hardware logic circuitry, which may be implemented by an ASIC or the FPGA circuitry  1800  of  FIG.  18    structured to perform operations corresponding to the machine readable instructions. Additionally or alternatively, the at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , or the datastore  270  may be instantiated by any other combination of hardware, software, and/or firmware. For example, the at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , or the datastore  270  may be implemented by at least one or more hardware circuits (e.g., processor circuitry, discrete and/or integrated analog and/or digital circuitry, an FPGA, an Application Specific Integrated Circuit (ASIC), a comparator, an operational-amplifier (op-amp), a logic circuit, etc.) structured to execute some or all of the machine readable instructions and/or to perform some or all of the operations corresponding to the machine readable instructions without executing software or firmware, but other structures are likewise appropriate. 
     In some examples, the means for encoding is to encode a first symbol in a media file at a first symbol position on a first encoding layer of a multilayered watermark, and encode a second symbol in the media file at a second symbol position on a second encoding layer of the multilayered watermark, the first encoding layer and the second encoding layer including a plurality of symbol positions, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     In some examples, the means for encoding includes means for identifying a media file as scheduled to be accessed by a media device after a publishing of the media file by a media provider. In some examples, the means for identifying may be implemented by the media identification generator circuitry  220 . 
     In some examples, in response to identifying the media file as scheduled to be accessed by the media device within a first time period after the publishing of the media file, the means for encoding is to select the first symbol to be inserted at the first symbol position and the second symbol to be inserted at the second symbol position to identify an access of the media filed by the media device within the first time period. For example, the means for encoding may include means for selecting the first symbol and the second symbol. In some such examples, the means for selecting may be implemented by at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260 . 
     In some examples, in response to identifying the media file as scheduled to be accessed by the media device within a second time period after the publishing of the media file, the means for encoding is to select the first symbol to be inserted at a third symbol position on the first encoding layer and the second symbol to be inserted at a fourth symbol position on the second encoding layer, encode the first symbol in the media file at the third symbol position on the first encoding layer, and encode the second symbol in the media file at the fourth symbol position on the second encoding layer, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     In some examples, the means for encoding is to encode a first bit sequence in a media file on a first encoding layer of a multilayered watermark, the first bit sequence to include one or more first bits associated with a timestamp of the multilayered watermark, and encode a second bit sequence in the media file on a second encoding layer of the multilayered watermark, the second bit sequence to include (i) one or more second bits associated with the timestamp and (ii) one or more third bits. 
     In some examples, the means for encoding includes means for converting to convert the timestamp in a first format to a second format, the first format based on a number of seconds at which the multilayered watermark is to be encoded in the media file, the second format based on a number of minutes at which the multilayered watermark is to be encoded in the media file, and convert the timestamp in the second format to a third bit sequence, the first bit sequence corresponding to one or more least significant bits of the third bit sequence, the second bit sequence corresponding to one or more most significant bits of the third bit sequence. In some such examples, the means for converting may be implemented by the timestamp generator circuitry  240 . 
     In some examples, the means for encoding includes means for determining to determine a first value based on the timestamp and a range of timestamps, determine a second value based on the timestamp, the first value, and the range of timestamps, and convert the second value into the first bit sequence. In some such examples, the means for determining is to determine a third value based on a sum of the first value and the second value, convert the third value into a third bit sequence, and determine the one or more third bits by shifting the third bit sequence by an offset value. In some such examples, the means for determining may be implemented by the timestamp generator circuitry  240 . 
     In some examples, the means for encoding includes means for determining to determine a third value based on a multiplication of the first value and a fourth value, determine a fifth value based on a sum of the third value and a parity value, the parity value to be converted into the one or more third bits, and convert the fifth value into the one or more second bits. In some such examples, the means for determining may be implemented by the timestamp generator circuitry  240 . 
     In some examples in which the media file is to be encoded with a plurality of multilayered watermarks with associated timestamps, successive ones of the timestamps to be incremented at a minute level, the plurality of the multilayered watermarks including the multilayer watermark, the timestamps including the timestamp, the means for encoding includes means for incrementing to increment successive ones of the plurality of the timestamps at the minute level, and in response to the incrementing of the successive ones of the plurality of the timestamps, increment the first bit sequence and the second bit sequence of respective ones of the successive ones of the plurality of the timestamps. In some such examples, the means for incrementing may be implemented by the timestamp generator circuitry  240 . 
     While an example manner of implementing the watermark encoder  106  of  FIG.  1    is illustrated in  FIG.  2   , one or more of the elements, processes, and/or devices illustrated in  FIG.  2    may be combined, divided, re-arranged, omitted, eliminated, and/or implemented in any other way. Further, the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , the datastore  270 , the bus  280 , and/or, more generally, the example watermark encoder  106  of  FIG.  1   , may be implemented by hardware, software, firmware, and/or any combination of hardware, software, and/or firmware. Thus, for example, any of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , the datastore  270 , the bus  280 , and/or, more generally, the example watermark encoder  106 , could be implemented by processor circuitry, analog circuit(s), digital circuit(s), logic circuit(s), programmable processor(s), programmable microcontroller(s), graphics processing unit(s) (GPU(s)), digital signal processor(s) (DSP(s)), application specific integrated circuit(s) (ASIC(s)), programmable logic device(s) (PLD(s)), and/or field programmable logic device(s) (FPLD(s)) such as Field Programmable Gate Arrays (FPGAs). When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the interface circuitry  210 , the media identification generator circuitry  220 , the SID generator circuitry  230 , the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250 , the sparse watermark embedder circuitry  260 , the datastore  270 , and/or the bus  280  is/are hereby expressly defined to include a non-transitory computer readable storage device or storage disk such as a memory, a DVD, a CD, a Blu-ray disk, etc., including the software and/or firmware. Further still, the example watermark encoder  106  of  FIG.  1    may include one or more elements, processes, and/or devices in addition to, or instead of, those illustrated in  FIG.  2   , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
       FIG.  3    is a block diagram of an example implementation of the first example watermark decoder  124  of  FIG.  1    and/or the second example watermark decoder  127  of  FIG.  1    to decode media that is embedded with multilayered watermarks. The watermark decoder  124 ,  127  of  FIG.  3    may be instantiated by processor circuitry such as a central processing unit executing instructions. Additionally or alternatively, the watermark decoder  124 ,  127  of  FIG.  3    may be instantiated by an ASIC or an FPGA structured to perform operations corresponding to the instructions. 
     The watermark decoder  124 ,  127  of  FIG.  3    includes example interface circuitry  310 , example watermark detector circuitry  320 , example media identification determiner circuitry  330 , example source identification (SID) determiner circuitry  340 , example timestamp determiner circuitry  350 , an example datastore  370 , and an example bus  380 . In this example, the datastore  370  includes example identifiers  374 , example timestamps  376 , and example watermarks  378 . In the illustrated example, the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp determiner circuitry  350 , and the datastore  370  is/are in communication with one(s) of each other by the bus  380 . For example, the bus  380  may be implemented by at least one of an I2C bus, a SPI bus, a PCI, and/or a PCIe bus. Additionally or alternatively, the bus  380  may implement any other type of computing or electrical bus. 
     The watermark decoder  124 ,  127  of the illustrated example includes the interface circuitry  310  to receive and/or transmit data. In some examples, the interface circuitry  310  receives and/or otherwise obtains data from the AME  104 , which may include firmware and/or software updates to one or more components of the watermark decoder  124 ,  127 . In some examples, the interface circuitry  310  may transmit the identifiers  374 , the timestamps  376 , or the watermarks  378  to the AME  104  of  FIG.  1    via the second network  110 . In some examples, the interface circuitry  310  may implement a web server that receives data from the AME  104 . In some examples, the interface circuitry  310  may implement a web server that transmits data to the AME  104 . In some examples, the interface circuitry  310  may receive and/or transmit data formatted as an HTTP message. However, any other message format and/or protocol may additionally or alternatively be used such as, for example, FTP, SMTP, HTTPS protocol, etc. In some examples, the interface circuitry  310  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a USB interface, a Bluetooth® interface, an NFC interface, a PCI interface, and/or a PCIe interface. 
     The watermark decoder  124 ,  127  of the illustrated example includes the watermark detector circuitry  320  to detect a watermark associated with media (e.g., the media  272 ) accessed and/or presented by the media presentation device  112  of  FIG.  1   . In some examples, the watermark detector circuitry  320  determines that encoded media is accessed/presented by the media presentation device  112  in response to a detection of a watermark embedded in audio generated by the audio devices  132  of  FIG.  1   . In some examples, the watermark detector circuitry  320  extracts watermarks from the audio. For example, the watermark detector circuitry  320  may extract a dense single or multilayer watermark, a sparse single or multilayer watermark, etc., from the audio. 
     In some examples, the watermark detector circuitry  320  identifies symbol(s) at symbol position(s). For example, the watermark detector circuitry  320  may identify a first symbol at a first symbol position of a first encoding layer of a multilayer watermark, a second symbol at a second symbol position of a second encoding layer of the multilayer watermark, etc. In some examples, the watermark detector circuitry  320  determines whether to continue monitoring for access of encoded media by device(s) based on whether additional watermarks have been detected from the audio. 
     The watermark decoder  124 ,  127  of the illustrated example includes the media identification determiner circuitry  330  to determine whether a media identifier is identified based on a watermark. For example, the media identification determiner circuitry  330  may determine that a watermark includes a media identifier that identifies media based on detected symbol(s), symbol position(s) of the detected symbol(s), etc. In some such examples, the media identification determiner circuitry  330  may identify the media based on the media identifier. 
     The watermark decoder  124 ,  127  of the illustrated example includes the SID determiner circuitry  340  to determine whether a SID is identified based on a watermark. For example, the SID determiner circuitry  340  may determine that a watermark includes a SID that identifies a provider of the accessed media based on detected symbol(s), symbol position(s) of the detected symbol(s), etc. In some such examples, the SID determiner circuitry  340  may identify the provider of the accessed media based on the SID. 
     The watermark decoder  124 ,  127  of the illustrated example includes the timestamp determiner circuitry  350  to determine whether a timestamp is identified based on a watermark. For example, the timestamp determiner circuitry  350  may determine that a watermark includes timestamp data that identifies a portion of the media that the media presentation device  112  is presenting based on detected symbol(s), symbol position(s) of the detected symbol(s), etc. In some examples, the timestamp determiner circuitry  350  may determine a timestamp based on timestamp data that is encoded on multiple layers of a multilayer watermark. For example, the timestamp determiner circuitry  350  may identify a first bit sequence on a first encoding layer of a multilayer watermark and a second bit sequence on a second encoding layer of the multilayer watermark. In some such examples, the timestamp determiner circuitry  350  may assemble, compile, and/or otherwise determine the timestamp encoded in the media based on the first bit sequence, the second bit sequence, etc., and/or combination(s) thereof 
     In some examples, the timestamp determiner circuitry  350  may check, verify, and/or otherwise validate that the decoded timestamp is correct based on one or more error check or parity bits included in at least one of the first bit sequence or the second bit sequence. For example, the first bit sequence and/or the second bit sequence may include one or more parity bits that, when decoded, may be used by the timestamp determiner circuitry  350  to determine whether the timestamp is a valid timestamp. 
     In some examples, the timestamp determiner circuitry  350  may determine that one(s) of the watermark symbols convey a state (e.g., a media state) of accessed media. For example, the timestamp determiner circuitry  350 , based on a symbol position and/or encoding layer of one or more watermark symbols, may determine that the one or more watermark symbols convey and/or identify a first state (e.g., a first media state). In some such examples, the first state may correspond to media being accessed and/or presented within a first time period after an initial publishing of the media. In some such examples, the timestamp determiner circuitry  350  may determine that the one or more watermark symbols (e.g., encoding layer(s) and/or symbol position(s) associated with the one or more watermark symbols) indicate that the accessed/presented media has the first state. In some such examples, the timestamp determiner circuitry  350  may determine that the first state implements a C 3  media state, which may indicate that the accessed/presented RTVOD media is being accessed/presented within three days of the initial publishing. 
     In some examples, the timestamp determiner circuitry  350 , based on a symbol position and/or encoding layer of one or more watermark symbols, may determine that the one or more watermark symbols convey and/or identify a second state (e.g., a second media state). In some such examples, the second state may correspond to media being accessed and/or presented within a second time period after an initial publishing of the media. In some such examples, the timestamp determiner circuitry  350  may determine that the one or more watermark symbols (e.g., encoding layer(s) and/or symbol position(s) associated with the one or more watermark symbols) indicate that the accessed/presented media has the second state. In some such examples, the timestamp determiner circuitry  350  may determine that the second state implements a C7 media state, which may indicate that the accessed/presented RTVOD media is being accessed/presented within seven days of the initial publishing. In some examples, at least one of the watermark detector circuitry  320 , the media identification determiner circuitry  330 , and/or the SID determiner circuitry  340  may determine that the one or more watermark symbols indicate the first media state, the second media state, etc. 
     The watermark decoder  124 ,  127  of the illustrated example includes the datastore  370  to record data (e.g., the identifiers  374 , the timestamps  376 , the watermarks  378 , the media state(s), etc.). For example, the datastore  370  may store the identifiers  374 , which may include identifiers (e.g., media identifiers, SIDs, etc.) extracted from a watermark by the watermark detector circuitry  320  and/or identified by the media identification determiner circuitry  330 . The datastore  370  may store the timestamps  376  determined by the timestamp determiner circuitry  350 . The datastore  370  may store the watermarks  378  extracted by the watermark detector circuitry  320 . 
     The datastore  370  may be implemented by a volatile memory (e.g., an SDRAM, a DRAM, an RDRAM, etc.) and/or a non-volatile memory (e.g., flash memory). The datastore  370  may additionally or alternatively be implemented by one or more DDR memories, such as DDR, DDR2, DDR3, DDR4, mDDR, etc. The datastore  370  may additionally or alternatively be implemented by one or more mass storage devices such as HDD(s), CD drive(s), DVD drive(s), SSD drive(s), etc. While in the illustrated example the datastore  370  is illustrated as a single datastore, the datastore  370  may be implemented by any number and/or type(s) of datastores. Furthermore, the data stored in the datastore  370  may be in any data format such as, for example, binary data, comma delimited data, tab delimited data, SQL structures, etc. In some examples, the datastore  370  implements one or more databases. 
     In some examples, the watermark decoder  124 ,  127  includes means for decoding media. For example, the means for decoding may be implemented by at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp generator circuitry  350 , or the datastore  370 . In some examples, the at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp generator circuitry  350 , or the datastore  370  may be instantiated by processor circuitry such as the example processor circuitry  1412  of  FIG.  14   . For instance, the at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp generator circuitry  350 , or the datastore  370  may be instantiated by the example general purpose processor circuitry  1700  of  FIG.  17    executing machine executable instructions such as that implemented by at least blocks  1010 ,  1012 ,  1014 ,  1016 ,  1018 ,  1022  of  FIG.  10    and/or blocks  1210 ,  1212 ,  1214 ,  1216 ,  1220  of  FIG.  12   . In some examples, the at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp generator circuitry  350 , or the datastore  370  may be instantiated by hardware logic circuitry, which may be implemented by an ASIC or the FPGA circuitry  1800  of  FIG.  18    structured to perform operations corresponding to the machine readable instructions. Additionally or alternatively, the at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp generator circuitry  350 , or the datastore  370  may be instantiated by any other combination of hardware, software, and/or firmware. For example, the at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp generator circuitry  350 , or the datastore  370  may be implemented by at least one or more hardware circuits (e.g., processor circuitry, discrete and/or integrated analog and/or digital circuitry, an FPGA, an Application Specific Integrated Circuit (ASIC), a comparator, an operational-amplifier (op-amp), a logic circuit, etc.) structured to execute some or all of the machine readable instructions and/or to perform some or all of the operations corresponding to the machine readable instructions without executing software or firmware, but other structures are likewise appropriate. 
     In some examples, the means for decoding is to, in response to an access of the media file by a media device, extract the multilayered watermark from audio of the media file, identify the first symbol at the first symbol position and the second symbol at the second symbol position, determine that the media file is accessed within a first time period or a second time period after a publishing of the media file by a media provider based on the first symbol at the first symbol position and the second symbol at the second symbol position, and provide an indication to a server that the media file is accessed within the first time period or the second time period. 
     While an example manner of implementing the first watermark decoder  124  of  FIG.  1    and/or the second watermark decoder  127  of  FIG.  1    is illustrated in  FIG.  3   , one or more of the elements, processes, and/or devices illustrated in  FIG.  3    may be combined, divided, re-arranged, omitted, eliminated, and/or implemented in any other way. Further, the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp determiner circuitry  350 , the datastore  370 , the bus  380 , and/or, more generally, the first watermark decoder  124  of  FIG.  1    and/or the second watermark decoder  127  of  FIG.  1   , may be implemented by hardware, software, firmware, and/or any combination of hardware, software, and/or firmware. Thus, for example, any of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp determiner circuitry  350 , the datastore  370 , the bus  380 , and/or, more generally, the first watermark decoder  124  of  FIG.  1    and/or the second watermark decoder  127  of  FIG.  1   , could be implemented by processor circuitry, analog circuit(s), digital circuit(s), logic circuit(s), programmable processor(s), programmable microcontroller(s), GPU(s), DSP(s), ASIC(s), PLD(s), and/or FPLD(s) such as FPGAs. When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the interface circuitry  310 , the watermark detector circuitry  320 , the media identification determiner circuitry  330 , the SID determiner circuitry  340 , the timestamp determiner circuitry  350 , the datastore  370 , and/or the bus  380  is/are hereby expressly defined to include a non-transitory computer readable storage device or storage disk such as a memory, a DVD, a CD, a Blu-ray disk, etc., including the software and/or firmware. Further still, the first watermark decoder  124  of  FIG.  1    and/or the second watermark decoder  127  of  FIG.  1    may include one or more elements, processes, and/or devices in addition to, or instead of, those illustrated in  FIG.  3   , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
       FIG.  4    is a block diagram of an example implementation of the example AME  104  of  FIG.  1    to associate accessed media with demographics (e.g., demographic data) of users based on multilayered watermarks embedded in the accessed media. The AME  104  of  FIG.  4    may be instantiated by processor circuitry such as a central processing unit executing instructions. Additionally or alternatively, the AME  104  of  FIG.  4    may be instantiated by an ASIC or an FPGA structured to perform operations corresponding to the instructions. 
     The AME  104  of the illustrated example includes example interface circuitry  410 , example watermark detector circuitry  420 , example media identification determiner circuitry  430 , example source identification (SID) determiner circuitry  440 , example timestamp determiner circuitry  450 , example demographic associator circuitry  460 , an example datastore  470 , and an example bus  490 . In this example, the datastore  470  includes example media  472 , example identifiers  474 , example timestamps  476 , example watermarks  478 , and example demographic data  480 . The interface circuitry  410 , the watermark detector circuitry  420 , the media identification determiner circuitry  430 , the SID determiner circuitry  440 , the timestamp determiner circuitry  450 , the demographic associator circuitry  460 , and the datastore  470  is/are in communication with one(s) of each other by the bus  490 . For example, the bus  490  may be implemented by at least one of an I2C bus, a SPI bus, a PCI, and/or a PCIe bus. Additionally or alternatively, the bus  490  may implement any other type of computing or electrical bus. 
     The AME  104  of the illustrated example includes the interface circuitry  410  to receive and/or transmit data. In some examples, the interface circuitry  410  receives and/or otherwise obtains data from the media provider  102  and/or the watermark encoder  106 , which may include the media  472 . In some examples, the interface circuitry  410  may transmit the identifiers  474  and/or the timestamps  476  to the media provider  102  and/or the watermark encoder  106 . In some examples, the interface circuitry  410  may receive the identifiers  474 , the timestamps  476 , and/or the watermarks  478  from the first meter  120  and/or the second meter  126  via the second network  110 . In some examples, the AME  104  may transmit the demographic data  480  to the media provider  102 . 
     In some examples, the interface circuitry  410  may implement a web server that receives and/or transmits data. In some examples, the interface circuitry  410  may receive and/or transmit data formatted as an HTTP message. However, any other message format and/or protocol may additionally or alternatively be used such as, for example, FTP, SMTP, HTTPS protocol, etc. In some examples, the interface circuitry  410  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a USB interface, a Bluetooth® interface, an NFC interface, a PCI interface, and/or a PCIe interface. 
     The AME  104  of the illustrated example includes the watermark detector circuitry  420  to detect a watermark associated with media (e.g., the media  472 ) accessed by the media presentation device  112  of  FIG.  1   . In some examples, the watermark detector circuitry  420  determines that encoded media is accessed by the media presentation device  112  in response to a detection of a watermark embedded in audio generated by the audio devices  132  of  FIG.  1   . In some examples, the watermark detector circuitry  420  extracts watermarks from the audio. For example, the watermark detector circuitry  420  may extract a dense single or multilayer watermark, a sparse single or multilayer watermark, etc., from the audio. In some such examples, the first meter  120  and/or the second meter  126  may provide an audio sample or portion to the AME  104 , and the watermark detector circuitry  420  may extract a watermark from the audio sample or portion. 
     In some examples, the watermark detector circuitry  420  identifies symbol(s) at symbol position(s). For example, the watermark detector circuitry  420  may identify a first symbol at a first symbol position of a first encoding layer of a multilayer watermark, a second symbol at a second symbol position of a second encoding layer of the multilayer watermark, etc. In some examples, the watermark detector circuitry  420  determines whether to continue monitoring for access of encoded media by device(s) based on whether additional watermarks have been received by the interface circuitry  410 . 
     The AME  104  of the illustrated example includes the media identification determiner circuitry  430  to determine whether a media identifier is included in a watermark. For example, the media identification determiner circuitry  430  may determine that a watermark includes a media identifier that identifies the media  472  based on detected symbol(s), symbol position(s) of the detected symbol(s), etc. In some such examples, the media identification determiner circuitry  430  may identify the media  472  based on the media identifier. 
     The AME  104  of the illustrated example includes the SID determiner circuitry  440  to determine whether a SID is identified based on a watermark. For example, the SID determiner circuitry  440  may determine that a watermark includes a SID that identifies a provider of the accessed media based on detected symbol(s), symbol position(s) of the detected symbol(s), etc. In some such examples, the SID determiner circuitry  440  may identify the provider of the accessed media based on the SID. 
     The AME  104  of the illustrated example includes the timestamp determiner circuitry  450  to determine whether a timestamp is identified based on a watermark. For example, the timestamp determiner circuitry  450  may determine that a watermark includes timestamp data that identifies a portion of the media that the media presentation device  112  is presenting based on detected symbol(s), symbol position(s) of the detected symbol(s), etc. In some examples, the timestamp determiner circuitry  450  may determine a timestamp based on timestamp data that is encoded on multiple layers of a multilayer watermark. For example, the timestamp determiner circuitry  450  may identify a first bit sequence on a first encoding layer of a multilayer watermark and a second bit sequence on a second encoding layer of the multilayer watermark. In some such examples, the timestamp determiner circuitry  450  may assemble, compile, and/or otherwise determine the timestamp encoded in the media based on the first bit sequence, the second bit sequence, etc., and/or combination(s) thereof 
     In some examples, the timestamp determiner circuitry  450  may check, verify, and/or otherwise validate that the decoded timestamp is correct based on one or more error check or parity bits included in at least one of the first bit sequence or the second bit sequence. For example, the first bit sequence and/or the second bit sequence may include one or more parity bits that, when decoded, may be used by the timestamp determiner circuitry  450  to determine whether the timestamp is a valid timestamp. 
     In some examples, the timestamp determiner circuitry  450  may determine that one(s) of the watermark symbols convey a state (e.g., a media state) of accessed media. For example, the timestamp determiner circuitry  450 , based on a symbol position and/or encoding layer of one or more watermark symbols, may determine that the one or more watermark symbols convey and/or identify a first state (e.g., a first media state). In some such examples, the first state may correspond to media being accessed and/or presented within a first time period after an initial publishing of the media. In some such examples, the timestamp determiner circuitry  450  may determine that the one or more watermark symbols (e.g., encoding layer(s) and/or symbol position(s) associated with the one or more watermark symbols) indicate that the accessed/presented media has the first state. In some such examples, the timestamp determiner circuitry  450  may determine that the first state implements a C3 media state, which may indicate that the accessed/presented RTVOD media is being accessed/presented within three days of the initial publishing. 
     In some examples, the timestamp determiner circuitry  450 , based on a symbol position and/or encoding layer of one or more watermark symbols, may determine that the one or more watermark symbols convey and/or identify a second state (e.g., a second media state). In some such examples, the second state may correspond to media being accessed and/or presented within a second time period after an initial publishing of the media. In some such examples, the timestamp determiner circuitry  450  may determine that the one or more watermark symbols (e.g., encoding layer(s) and/or symbol position(s) associated with the one or more watermark symbols) indicate that the accessed/presented media has the second state. In some such examples, the timestamp determiner circuitry  450  may determine that the second state implements a C7 media state, which may indicate that the accessed/presented RTVOD media is being accessed/presented within seven days of the initial publishing. In some examples, at least one of the watermark detector circuitry  420 , the media identification determiner circuitry  430 , and/or the SID determiner circuitry  440  may determine that the one or more watermark symbols indicate the first media state, the second media state, etc. 
     The AME  104  of the illustrated example includes the demographic associator circuitry  460  to associate demographics and accessed one(s) of the media  472 . For example, a plurality of panelists including the panelist  116  at the monitored site  130  may have provided their respective demographics to the AME  104 . In some such examples, the demographic associator circuitry  460  may receive the demographic data  480  via a personal interview (by telephone or in person), a telephone interface, direct mailing, purchased lists, etc. Additionally or alternatively, the demographic data  480  may be obtained manually by a person or group of people collecting and entering the registration data into the datastore  470 . 
     In some examples, the demographic data  480  includes information identifying the model of the first panelist device  114  and/or the second panelist device  118  associated with the panelist  116 , a mailing address associated with the panelist  116 , an email address associated with the panelist  116 , a phone number associated with a mobile device of the panelist  116 , a unique identifier of the panelist  116 , the first panelist device  114 , and/or the second panelist device  118  (e.g., a social security number of the panelist  116 , a phone number of a mobile device associated with the panelist  116 , a zip code of the panelist  116 , and/or any combination or derivation of any information related to the panelist  116  and/or the mobile device), the age of the panelist  116 , the gender of the panelist  116 , the race of the panelist  116 , the marital status of the panelist  116 , the income of the panelist  116  and/or the household of the panelist  116 , the employment status of the panelist  116 , where the panelist  116  typically intend to access the media  472 , how long the panelist  116  typically accesses the media  472 , the education level of the panelist  116 , and/or any other information related to the panelist  116 . 
     In some examples, the demographic associator circuitry  460  may prepare and/or otherwise generate a report associating the demographic data and the accessed one(s) of the media  472 . In some examples, the demographic associator circuitry  460  may generate a report identifying demographics associated with the panelist  116  via received monitoring information (e.g., the identifiers  474 , the timestamps  476 , the watermarks  478 , etc.) from the first meter  120  and/or the second meter  126 . For example, the demographic associator circuitry  460  may generate a report associating the demographic data  480  of the panelist  116  with accessed one(s) of the media  472 . For example, the demographic associator circuitry  460  may credit the media  472  as having been accessed by the panelist  116  by way of the media presentation device  112  of  FIG.  1   . 
     The AME  104  of the illustrated example includes the datastore  470  to record data (e.g., the media  472 , the identifiers  474 , the timestamps  476 , the watermarks  478 , the demographic data  480 , the media state(s), etc.). For example, the datastore  470  may store the media  472  obtained from the media provider  102 , the first meter  120 , and/or the second meter  126 . The datastore  470  may store the identifiers  474 , which may include identifiers (e.g., media identifiers, SIDs, etc.) obtained from the first meter  120  and/or the second meter  126 . In some examples, the datastore  470  may store the identifiers  474  extracted from a watermark by the watermark detector circuitry  420  and/or identified by the media identification determiner circuitry  430 . The datastore  470  may store the timestamps  476  obtained from the first meter  120  and/or the second meter  126 . In some examples, the datastore  470  may store the timestamps  476  determined by the timestamp determiner circuitry  450 . The datastore  470  may store the watermarks  478  obtained from the first meter  120  and/or the second meter  126 . In some examples, the datastore  470  stores the watermarks  478  extracted by the watermark detector circuitry  420 . 
     The datastore  470  may be implemented by a volatile memory (e.g., an SDRAM, a DRAM, an RDRAM, etc.) and/or a non-volatile memory (e.g., flash memory). The datastore  470  may additionally or alternatively be implemented by one or more DDR memories, such as DDR, DDR2, DDR3, DDR4, mDDR, etc. The datastore  470  may additionally or alternatively be implemented by one or more mass storage devices such as HDD(s), CD drive(s), DVD drive(s), SSD drive(s), etc. While in the illustrated example the datastore  470  is illustrated as a single datastore, the datastore  470  may be implemented by any number and/or type(s) of datastores. Furthermore, the data stored in the datastore  470  may be in any data format such as, for example, binary data, comma delimited data, tab delimited data, SQL structures, etc. In some examples, the datastore  470  implements one or more databases. 
     While an example manner of implementing the AME  104  of  FIG.  1    is illustrated in  FIG.  4   , one or more of the elements, processes, and/or devices illustrated in  FIG.  4    may be combined, divided, re-arranged, omitted, eliminated, and/or implemented in any other way. Further, the interface circuitry  410 , the watermark detector circuitry  420 , the media identification determiner circuitry  430 , the SID determiner circuitry  440 , the timestamp determiner circuitry  450 , the demographic associator circuitry  460 , the datastore  470 , the bus  490 , and/or, more generally, the example AME  104  of  FIG.  1   , may be implemented by hardware, software, firmware, and/or any combination of hardware, software, and/or firmware. Thus, for example, any of the interface circuitry  410 , the watermark detector circuitry  420 , the media identification determiner circuitry  430 , the SID determiner circuitry  440 , the timestamp determiner circuitry  450 , the demographic associator circuitry  460 , the datastore  470 , the bus  490 , and/or, more generally, the example AME  104 , could be implemented by processor circuitry, analog circuit(s), digital circuit(s), logic circuit(s), programmable processor(s), programmable microcontroller(s), GPU(s), DSP(s), ASIC(s), PLD(s), and/or FPLD(s) such as FPGAs. When reading any of the apparatus or system claims of this patent to cover a purely software and/or firmware implementation, at least one of the interface circuitry  410 , the watermark detector circuitry  420 , the media identification determiner circuitry  430 , the SID determiner circuitry  440 , the timestamp determiner circuitry  450 , the demographic associator circuitry  460 , the datastore  470 , and/or the bus  490  is/are hereby expressly defined to include a non-transitory computer readable storage device or storage disk such as a memory, a DVD, a CD, a Blu-ray disk, etc., including the software and/or firmware. Further still, the example AME  104  of  FIG.  1    may include one or more elements, processes, and/or devices in addition to, or instead of, those illustrated in  FIG.  4   , and/or may include more than one of any or all of the illustrated elements, processes and devices. 
       FIG.  5    depicts example watermarks  502 ,  504 ,  506 ,  508 ,  510  in encoded media  500  at different example frequency layers  512 ,  514 ,  516 ,  518 . In some examples, one(s) of the watermarks  502 ,  504 ,  506 ,  508 ,  510  may be implemented by the watermarks  278  of  FIG.  2   , the watermarks  378  of  FIG.  3   , and/or the watermarks  478  of  FIG.  4   . The frequency layers  512 ,  514 ,  516 ,  518  may correspond to respective ranges of frequencies at which the watermarks  502 ,  504 ,  506 ,  508 ,  510  are to be encoded. For example, the first frequency layer  512  (identified by LAYER 1) may be implemented by a first range of frequencies, the second frequency layer  512  (identified by LAYER 2) may be implemented by a second range of frequencies, etc., so that the first range of frequencies and the second range of frequencies do not overlap. In some examples, the watermarks  502 ,  504 ,  506 ,  508 ,  510  may be encoded based on Reed-Solomon (RS) codes. For example, the frequency layers  512 ,  514 ,  516 ,  518  may be implemented by RS frequency layers. In some such examples, the first watermarks  502  may correspond to RS Layer 1 (L1) watermarks, the second watermarks  504  may correspond to RS Layer 2 (L2) watermarks, etc. Advantageously, the watermarks  502 ,  504 ,  506 ,  508 ,  510  may be encoded using frequency division multiplexing because of the different frequency layers  512 ,  514 ,  516 ,  518 . 
     In some examples, the encoded media  500  may be a media file encoded by the watermark encoder  106  of  FIG.  1   . For example, the watermark encoder  106  may encode the first frequency layer  512  with the first watermarks  502 , the second frequency layer  514  with the second watermarks  504 , etc. In the illustrated example, the watermark encoder  106  may generate dense watermarks. For example, the watermark encoder  106  may generate the first watermarks  502  as dense single layer watermarks by generating the first watermarks  502  as having a single encoding layer in which all or a substantial portion of symbol positions of the first watermarks  502  are filled with symbols. In some examples, the watermark encoder  106  may generate the second watermarks  504  and the fifth watermarks  510  as dense single layer watermarks. In some examples, the watermark encoder  106  may generate the third watermarks  506  as dense multilayered watermarks by generating the third watermarks  506  as having at least a first layer (LAYER A) and a second layer (LAYER B) in which all or a substantial portion of symbol positions of the first layer and the second layer are filled with symbols. 
     In some examples, the watermark encoder  106  may generate watermarks at the fourth frequency layer  516  that indicate different states of media presentation. For example, the watermark encoder  106  may generate the third watermarks  506  to indicate whether presented media is a television program, a commercial, etc., by encoding identifiers that identify media (e.g., a first identifier that identifies presented media as a television program, a second identifier that identifies presented media as a commercial, etc.). In some examples, the watermark encoder  106  may generate the fourth watermarks  508  to convey on-demand media access states, such as RTVOD media access states. For example, the watermark encoder  106  may generate the fourth watermarks  508  to indicate on-demand media access states by encoding a pattern of symbols across the multiple layers of the fourth watermarks  508 . In some such examples, the watermark encoder  106  may encode the pattern to indicate a first on-demand media access state that the encoded media  500  is to be accessed within a first time period (e.g., within three days after a premiere of the encoded media  500  for access by viewers on-demand). In some examples, the watermark encoder  106  may encode the pattern to indicate a second on-demand media access state that the encoded media  500  is to be accessed within a second time period (e.g., within seven days after a premiere of the encoded media  500  for access by viewers on-demand), etc. 
     In the illustrated example, the watermark encoder  106  may generate sparse watermarks. For example, the watermark encoder  106  may generate the fourth watermarks  508  as sparse multilayer watermarks by generating the fourth watermarks  508  as having at least a first layer (LAYER A) and a second layer (LAYER B) in which a substantial portion of symbol positions of the fourth watermarks  508  are not filled with a symbol. In some such examples, the watermark encoder  106  may generate the fourth watermarks  508  by inserting a first symbol at a first symbol position of a plurality of first symbol positions on the first encoding layer of a first one of the fourth watermarks  508  (identified by L4-RTVOD LAYER A) and a second symbol at a second symbol position of a plurality of second symbol positions on the second encoding layer on the first one of the fourth watermarks  508  (identified by L4-RTVOD LAYER B). In some such examples, the watermark encoder  106  may not insert a symbol at one or more symbol positions of the remaining first symbol positions and/or the remaining second symbol positions. 
       FIG.  6    depicts an example dense single-layer watermark  600  and an example dense multilayer watermark  620 . In some examples, the dense single-layer watermark  600  and/or the dense multilayer watermark  620  may implement one(s) of the watermarks  278  of  FIG.  2   , the watermarks  378  of  FIG.  3   , and/or the watermarks  478  of  FIG.  4   . In some examples, the dense single-layer watermark  600  may implement one(s) of the first watermarks  502 , the second watermarks  504 , and/or the fifth watermarks  510  of  FIG.  5   . In the illustrated example, the dense single-layer watermark  600  is placed on a single watermark encoding layer (e.g., an audio watermarking layer, an audio encoding layer, etc.). 
     In the illustrated example, the dense single-layer watermark  600  includes a first example bit sequence  610 , which includes first example symbols  612  (hereinafter  612 A,  612 B,  612 C,  612 D,  612 E,  612 F,  612 G,  612 H) at example symbol positions  614  (hereinafter symbol positions  0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ) during an example time window  616 . For example, the first symbols  612  are positioned in the dense single-layer watermark  600  to be substantially simultaneously read and/or parsed out from media. In other words, the first bit sequence  610  is to be simultaneously read and/or parsed in parallel by the first meter  120  and/or the second meter  126  of  FIG.  1   . 
     In this example, the first bit sequence  610  includes eight symbols. However, any appropriate number of bits and/or symbols can be implemented instead. Further, the first bit sequence  610  may be implemented on (e.g., embedded in) any appropriate file type including, but not limited to, audio files, video files, encoded transmissions, file downloads, etc. In the illustrated example, the dense single-layer watermark  600  is dense because there is a watermark symbol at each of the symbol positions. Alternatively, in some examples, the dense single-layer watermark  600  may be dense if there is a watermark symbol at a substantial number of the symbol positions. 
     In some examples, the dense multilayer watermark  620  may implement one(s) of the third watermarks  506  and/or the fourth watermarks  508  of  FIG.  5   . In the illustrated example, the dense multilayer watermark  620  is placed on multiple separate watermark encoding layers (e.g., separate audio watermarking layers, separate audio encoding layers, etc.). In some examples, a multilayer audio watermark, such as the dense multilayer watermark  620  of  FIG.  6   , can include multiple audio watermarking layers (also called audio encoding layers) in which different layers use frequency components from different frequency ranges or groups of frequency ranges (e.g., frequency components from different groups of frequency bins) of the audio signal/file to encode watermark symbols in their respective layers. For example, a first audio watermarking layer may use frequency components selected from a first group of frequency bins to encode a first set of watermark symbols in the audio signal/file, and a second audio watermarking layer may use frequency components selected from a second group of frequency bins to encode a second set of watermark symbols in the audio signal/file, with at least some of the frequency bins in the first and second groups being different. Advantageously, frequency components that have improved detection capability in acoustic environments may be selected to convey information (e.g., a media identifier, a timestamp, etc.) to increase a likelihood of detecting such a watermark. In the illustrated example, the dense multilayer watermark  620  includes a first example layer  622  (e.g., a first audio watermarking layer identified by LAYER A) and a second example layer  624  (e.g., a second audio watermarking layer identified by LAYER B). 
     In the illustrated example, the dense multilayer watermark  620  includes a second example bit sequence  630 , which includes second example symbols  632  (hereinafter  632 A,  632 B,  632 C,  632 D,  632 E,  632 F,  632 G,  632 H) at example symbol positions  634  (hereinafter symbol positions  0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ) during an example time window  636 . In the illustrated example, the dense multilayer watermark  620  includes a third example bit sequence  640 , which includes third example symbols  642  (hereinafter  642 A,  642 B,  642 C,  642 D,  642 E,  642 F,  642 G,  642 H) at example symbol positions  644  (hereinafter symbol positions  0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ) during the time window  636 . For example, the second symbols  632  and the third symbols  642  are positioned in the dense multilayer watermark  620  to be substantially simultaneously read and/or parsed out from media. In other words, the second bit sequence  630  and the third bit sequence  640  are to be simultaneously read and/or parsed in parallel by the first meter  120  and/or the second meter  126 . 
     In this example, the second bit sequence  630  and the third bit sequence  640  each include eight symbols. However, any appropriate number of bits and/or symbols can be implemented instead for the second bit sequence  630  and/or the third bit sequence  640 . Further, the second bit sequence  630  and/or the third bit sequence  640  may be implemented on (e.g., embedded in) any appropriate file type including, but not limited to, audio files, video files, encoded transmissions, file downloads, etc. In the illustrated example, the dense multilayer watermark  620  is dense because there is a watermark symbol at each of the symbol positions. Alternatively, in some examples, the dense multilayer watermark  620  may be dense if there is a watermark symbol at a substantial number of the symbol positions of the first layer  622  and/or the second layer  624 . 
       FIG.  7    depicts a first example sparse multilayer watermark  700  and a second example sparse multilayer watermark  730 . In some examples, the first sparse multilayer watermark  700  and/or the second sparse multilayer watermark  730  may implement one(s) of the watermarks  278  of  FIG.  2   , the watermarks  378  of  FIG.  3   , and/or the watermarks  478  of  FIG.  4   . In some examples, the first sparse multilayer watermark  700  and/or the second sparse multilayer watermark  730  may implement one(s) of the third watermarks  506  and/or the fourth watermarks  508  of  FIG.  5   . In the illustrated example, the first sparse multilayer watermark  700  and the second sparse multilayer watermark  730  are placed on multiple separate watermark encoding layers (e.g., separate audio watermarking layers, separate audio encoding layers, etc.) including a first example layer  702  (e.g., a first audio watermarking layer identified by LAYER A) and a second example layer  704  (e.g., a second audio watermarking layer identified by LAYER B). 
     In the illustrated example, the first sparse multilayer watermark  700  includes a first example bit sequence  710 , which includes a first example symbol  712  and a second example symbol  714  at respective ones of example symbol positions  716  (hereinafter symbol positions  0 ,  1 ,  2 ,  3 ,  4 ,  5 ,  6 ,  7 ) during an example time window  718 . In the illustrated example, the first sparse multilayer watermark  700  includes a second example bit sequence  720 , which includes a third example symbol  722  and a fourth example symbol  724  at respective ones of the symbol positions  716  during the time window  718 . 
     In the illustrated example, the first symbol  712  and the second symbol  714  are the same. Alternatively, the first symbol  712  and the second symbol  714  may be different from each other. In the illustrated example, the first symbol  712  is at and/or otherwise caused to be inserted at symbol position  0  of the first layer  702  and the second symbol  714  is at and/or otherwise caused to be inserted at symbol position  2  of the first layer  702 . In the illustrated example, the third symbol  722  and the fourth symbol  724  are the same. Alternatively, the third symbol  722  and the fourth symbol  724  may be different from each other. In the illustrated example, the third symbol  722  is at and/or otherwise caused to be inserted at symbol position  4  of the second layer  704  and the fourth symbol  724  is at and/or otherwise caused to be inserted at symbol position  7  of the second layer  704 . 
     In the illustrated example, the first bit sequence  710  and the second bit sequence  720  each include two symbols. However, any appropriate number of bits and/or symbols can be implemented instead for the first bit sequence  710  and/or the second bit sequence  720 . Further, the first bit sequence  710  and/or the second bit sequence  720  may be implemented on (e.g., embedded in) any appropriate file type including, but not limited to, audio files, video files, encoded transmissions, file downloads, etc. In the illustrated example, the first sparse multilayer watermark  700  is sparse because there is a watermark symbol missing at one or more of the symbol positions  716 . In this example, the first layer  702  is missing a watermark symbol at symbol positions  1 ,  3 ,  4 ,  5 ,  6 , and  7  while the second layer  704  is missing a watermark symbol at symbol positions  0 ,  1 ,  2 ,  3 ,  5 , and  6 . For example, symbol positions  1 ,  3 ,  4 ,  5 ,  6 , and  7  on the first layer  702  are empty because a watermark symbol is not encoded, embedded, etc., at those symbol positions. In the illustrated example, symbol positions  0 ,  1 ,  2 ,  3 ,  5 , and  6  on the second layer  704  are empty because a watermark symbol is not encoded, embedded, etc., at those symbol positions. Alternatively, the first layer  702  and/or the second layer  704  may have fewer or more empty symbol positions than depicted in the illustrated example. 
     In the illustrated example, the first symbol  712 , the second symbol  714 , the third symbol  722 , and the fourth symbol  724  are positioned amongst the symbol positions  716  of the first layer  702  and/or the second layer  704  to indicate a first media state. For example, the first meter  120  and/or the second meter  126  of  FIG.  1    may determine that media presented by the media presentation device  112  of  FIG.  1    is being accessed within a first time period of the media being made available on an on-demand platform. In some examples, the first sparse multilayer watermark  700  may implement a C3 watermark, which may indicate that media embedded with the first sparse multilayer watermark  700  is associated with media in the first media state of being accessed within three days (or a different number of days) after the media premiered on an on-demand platform. 
     In the illustrated example, the second sparse multilayer watermark  730  includes a third example bit sequence  740 , which includes a fifth example symbol  742  and a sixth example symbol  744  at a respective one of the symbol positions  716  during the time window  718 . In the illustrated example, the second sparse multilayer watermark  730  includes a third example bit sequence  750 , which includes a seventh example symbol  752  and an eighth example symbol  754  at a respective one of the symbol positions  716  during the time window  718 . 
     In the illustrated example, the fifth symbol  742  and the sixth symbol  744  are the same. Alternatively, the fifth symbol  742  and the sixth symbol  744  may be different from each other. In the illustrated example, the fifth symbol  742  is at and/or otherwise caused to be inserted at symbol position  3  of the first layer  702  and the sixth symbol  744  is at and/or otherwise caused to be inserted at symbol position  6  of the first layer  702 . In the illustrated example, the seventh symbol  752  and the eighth symbol  754  are the same. Alternatively, the seventh symbol  752  and the eighth symbol  754  may be different from each other. In the illustrated example, the seventh symbol  752  is at and/or otherwise caused to be inserted at symbol position  1  of the second layer  704  and the eighth symbol  754  is at and/or otherwise caused to be inserted at symbol position  5  of the second layer  704 . 
     In the illustrated example, the third bit sequence  740  and the fourth bit sequence  750  each include two symbols. However, any appropriate number of bits and/or symbols can be implemented instead for the third bit sequence  740  and/or the fourth bit sequence  750 . Further, the third bit sequence  740  and/or the fourth bit sequence  750  may be implemented on (e.g., embedded in) any appropriate file type including, but not limited to, audio files, video files, encoded transmissions, file downloads, etc. In the illustrated example, the second sparse multilayer watermark  730  is sparse because there is a watermark symbol missing at one or more of the symbol positions  716 . In this example, the first layer  702  is missing a watermark symbol at symbol positions  0 ,  1 ,  2 ,  4 ,  5 , and  7  the second layer  704  is missing a watermark symbol at symbol positions  0 ,  2 ,  3 ,  4 ,  6 , and  7 . For example, symbol positions  0 ,  1 ,  2 ,  4 ,  5 , and  7  on the first layer  702  are empty because a watermark symbol is not encoded, embedded, etc., at those symbol positions. In the illustrated example, symbol positions  0 ,  2 ,  3 ,  4 ,  6 , and  7  on the second layer  704  are empty because a watermark symbol is not encoded, embedded, etc., at those symbol positions. Alternatively, the first layer  702  and/or the second layer  704  may have fewer or more empty symbol positions than depicted in the illustrated example. 
     In the illustrated example, the fifth symbol  742 , the sixth symbol  744 , the seventh symbol  752 , and the eighth symbol  754  are positioned amongst the symbol positions  716  of the first layer  702  and/or the second layer  704  to indicate a second media state. For example, the first meter  120  and/or the second meter  126  of  FIG.  1    may determine that media presented by the media presentation device  112  of  FIG.  1    is being accessed within a second time period of the media being made available on an on-demand platform. In some examples, the second sparse multilayer watermark  730  may implement a C7 watermark, which may indicate that media embedded with the second sparse multilayer watermark  730  is associated with media in the first media state of being accessed within seven days (or a different number of days) after the media premiered on an on-demand platform. 
       FIG.  8    depicts an example single-layer watermark  800  that the first meter  120  and/or the second meter  126  may be configured to detect. In some examples, the single-layer watermark  800  may implement one(s) of the watermarks  278  of  FIG.  2   , the watermarks  378  of  FIG.  3   , and/or the watermarks  478  of  FIG.  4   . The single-layer watermark  800  of the illustrated is embedded or otherwise included in media to be presented by media device(s), such as the media presentation device  112  of  FIG.  1   . For example, the single-layer watermark  800  may be embedded in an audio portion (e.g., an audio data portion, an audio signal portion, etc.) of the media, a video portion (e.g., a video data portion, a video signal portion, etc.) of the media, or a combination thereof. The single-layer watermark  800  includes a first example group of symbols  805  and a second example group of symbols  810 . In some examples, the first group of symbols  805  may be repeated in successive watermarks  800  embedded/included in the media, whereas the second group of symbols  810  differs between successive watermarks  800  embedded/included in the media. 
     In the single-layer watermark  800  of the illustrated example, the first group of symbols  805  conveys media identification data (e.g., a media identifier identified by MEDIA ID) identifying the media watermarked by the single-layer watermark  800 . For example, the media identification data conveyed by the first group of symbols  805  may include data identifying a provider (e.g., a broadcast station, an on-demand media provider, a streaming media provider, etc.) providing the media, a name (e.g., program name) of the media, a source (e.g., a media platform, a website, etc.) of the media, etc. Thus, in the illustrated example, the first group of symbols  805  is also referred to as a first group of media identification symbols  805  (or simply the media identification symbols  805 ). Furthermore, in some examples, the media identification data conveyed by the first group of symbols  805  (e.g., the media identification symbols  805 ) may be repeated in successive single-layer watermarks  800  embedded/included in the media. 
     In some examples, the first group of symbols  805  of the single-layer watermark  800  includes example marker symbols  815 A,  815 B to assist the watermark decoders  124 ,  127  of  FIGS.  1  and/or  3    in detecting the start of the single-layer watermark  800  in the watermarked media, and example data symbols  820 A-F to convey the media identification data. Also, in some examples, corresponding symbols pairs in similar respective locations after the first marker symbol  815 A and the second marker symbol  815 B are related by an offset. For example, the value of data symbol  820 D may correspond to the value of data symbol  820 A incremented by an offset, the value of data symbol  820 E may correspond to the value of data symbol  820 B incremented by the same offset, and the value of data symbol  820 F may correspond to the value of data symbol  820 C incremented by the same offset, as well. 
     In the illustrated example, the second group of symbols  810  conveys timestamp data (e.g., a timestamp, a time-in content (TIC) value, etc.) identifying, for example, a particular elapsed time within the watermarked media. Thus, in the illustrated example, the second group of symbols  810  is also referred to as the second group of timestamp symbols  810  (or simply the timestamp symbols  810 ). Furthermore, in some examples, the timestamp data conveyed by the second group of symbols  810  (e.g., the timestamp symbols  810 ) differs in successive single-layer watermarks  800  embedded/included in the media (e.g., as the elapsed time of the watermarked media increases with each successive single-layer watermark  800 ). In some examples, the timestamp based on the timestamp symbols  810  may implement one(s) of the timestamps  276  of  FIG.  2   , the timestamps  376  of  FIG.  3   , and/or the timestamps  476  of  FIG.  4   . 
     In some examples, the single-layer watermark  800  is embedded/included in the desired media at a repetition interval of T seconds (or, in other words, at a repetition rate of 1/T seconds), with the first group of symbols  805  remaining the same in successive single-layer watermarks  800 , and the second group of symbols  810  varying in successive single-layer watermarks  800 . For example, the repetition interval T may correspond to T=4.8 seconds. As there are 12 symbols in the depicted single-layer watermark  800  (e.g., 8 symbols in the first group of symbols  805  and 4 symbols in the second group of symbols  810 ) each watermark symbol in the illustrated example has a duration of 4.8/12=0.4 seconds. However, other values for the repetition interval T may be used in other examples. 
     In some examples, a watermark symbol included in the single-layer watermark  800  is able to take on one of several possible symbol values. For example, if a symbol in the single-layer watermark  800  represents 4 bits of data, then the symbol is able to take on one of 16 different possible values. For example, each possible symbol value may correspond to a different signal amplitude, a different set of code frequencies, etc. In some such examples, to detect a watermark symbol embedded/included in watermarked media, the watermark decoders  124 ,  127  process monitored media data/signals output from the media presentation device  112  to determine measured values (e.g., signal-to-noise ratio (SNR) values) corresponding to each possible symbol value the symbol may have. The watermark decoders  124 ,  127  may then select the symbol value corresponding to the best (e.g., strongest, largest, etc.) measured value (possibly after averaging across multiple samples of the media data/signal) as the detected symbol value for that particular watermark symbol. 
       FIG.  9    depicts an example multilayer watermark  900  including first example symbols  902 , second example symbols  904 , and third example symbols  906  at example symbol positions  907  during an example time window  908 . In some examples, the multilayer watermark  900  may implement one(s) of the watermarks  278  of  FIG.  2   , the watermarks  378  of  FIG.  3   , and/or the watermarks  478  of  FIG.  4   . In this example, there are twelve of the symbol positions  907 . Alternatively, the multilayer watermark  900  may include fewer or more symbol positions. In this example, the first symbols  902  and the second symbols  904  are on the second frequency layer  514  of  FIG.  5   . Alternatively, the first symbols  902  and/or the second symbols  904  may be on a different frequency layer. In this example, the first symbols  902  and the third symbols  906  are on the fifth frequency layer  518  of  FIG.  5   . Alternatively, the first symbols  902  and/or the third symbols  906  may be on a different frequency layer. 
     In the illustrated example, the first symbols  902  implement an example media identifier  910  that identifies media that may be accessed and/or otherwise presented by the media presentation device  112  of  FIG.  1   . In the illustrated example, the first symbols  902  are inserted at symbol positions  0 - 7  of the symbol positions  907 . Alternatively, the first symbols  902  may be inserted, encoded, etc., at different one(s) of the symbol positions  907 . In the illustrated example, the first symbols  902  are the same in the second frequency layer  514  and the fifth frequency layer  518  so that the watermark decoders  124 ,  127  may identify that the second symbols  904  and the third symbols  906  are associated with each other and/or otherwise are to be processed in connection with each other. 
     In the illustrated example, the second symbols  904  and the third symbols  906  implement at least one of timestamp data or parity data. For example, the multilayer watermark  900  may implement a video-on demand (VOD) watermark that may be embedded in media accessible on a library VOD platform. In some such examples, the multilayer watermark  900  may include data to convey at least one of a media identifier that identifies media and timestamp data that identifies an elapsed time of the media. In the illustrated example, the second symbols  904  and the third symbols  906  are inserted, encoded, etc., at symbol positions  9 - 12  of the symbol positions  907 . Alternatively, the second symbols  904  and/or the third symbols  906  may be inserted at different one(s) of the symbol positions  907 . In some examples, the timestamp data may implement one(s) of the timestamps  276  of  FIG.  2   , the timestamps  376  of  FIG.  3   , and/or the timestamps  476  of  FIG.  4   . 
     In the illustrated example, the timestamp data may be encoded across multiple layers of the multilayer watermark  900 , such as the second frequency layer  514  and the fifth frequency layer  518  of  FIG.  5   . In some examples, the timestamp data may be encoded across multiple layers because the timestamp data may require a number of bits that exceeds a bandwidth of a single layer. For example, the timestamp data may require 30 is of data while each encoding layer may support 16 bits of data. In some such examples, the 30 bits of timestamp data can be supported by at least two encoding layers. 
     In some examples, the watermark encoder  106  of  FIG.  1    may encode the timestamp data across multiple layers of the multilayer watermark  900 . For example, the timestamp generator circuitry  240  of  FIG.  2    may determine a timestamp of the media and partition the timestamp into timestamp portions. In some such examples, the timestamp generator circuitry  240  may convert the timestamp data into a timestamp bitstream, and partition the timestamp bitstream into first bits and second bits. In some such examples, the timestamp generator circuitry  240  may identify the first bits as the least significant bits of the timestamp bitstream and the second bits as the most significant bits of the timestamp bitstream. For example, the timestamp generator circuitry  240  may identify the first bits as example timestamp least significant bits  912  and the second bits as a portion of example timestamp most significant bits and parity bits  914 . In some such examples, the timestamp generator circuitry  240  may generate the parity bits to facilitate error detection of decoding the multilayer watermark  900 . 
     In some examples, the timestamp generator circuitry  240  may determine the timestamp bitstream by obtaining a first timestamp in a time second format. For example, the timestamp may have a value of “150” to represent 150 seconds. In some examples, the timestamp generator circuitry  240  may convert the first timestamp in time second format to a second timestamp in time minute format. In some such examples, the time second format may implement a second level, a per-second increment basis, etc., (e.g., successive timestamps being incremented at the second level including a first timestamp of 18 seconds, a second timestamp of 19 seconds, a third timestamp of 20 seconds, etc.). In some such examples, the time minute format may implement a minute level, a per-minute increment basis, etc., (e.g., successive timestamps being incremented at the minute level including a first timestamp of 10 minutes, a second timestamp of 11 minutes, a third timestamp of 12 minutes, etc.). For example, the timestamp generator circuitry  240  may convert the first timestamp (timestamp minute ) into the second timestamp (timestamp second ) based on the example of Equation (1) below: 
     
       
         
           
             
               
                 
                   
                     
                       times 
                       ⁢ 
                       
                         tamp 
                         Minute 
                       
                     
                     = 
                     
                       floor 
                       ⁢ 
                           
                       
                         ( 
                         
                           
                             timestamp 
                             
                               s 
                               ⁢ 
                               e 
                               ⁢ 
                               c 
                               ⁢ 
                               o 
                               ⁢ 
                               n 
                               ⁢ 
                               d 
                             
                           
                           
                             6 
                             ⁢ 
                             0 
                           
                         
                         ) 
                       
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                   ⁢ 
                       
                   
                     ( 
                     1 
                     ) 
                   
                 
               
             
           
         
       
     
     In some examples, the timestamp generator circuitry  240  may determine the timestamp bitstream by determining a first value based on the second timestamp and a range of timestamps (timestamp range ) based on the example of Equation (2) below: 
     
       
         
           
             
               
                 
                   
                     
                       L 
                       ⁢ 
                       
                         2 
                         BASE 
                       
                     
                     = 
                     
                       floor 
                       ⁢ 
                           
                       
                         ( 
                         
                           
                             timestamp 
                             minute 
                           
                           
                             timestamp 
                             
                               r 
                               ⁢ 
                               a 
                               ⁢ 
                               n 
                               ⁢ 
                               g 
                               ⁢ 
                               e 
                             
                           
                         
                         ) 
                       
                     
                   
                   , 
                 
               
               
                 
                   Equation 
                   ⁢ 
                       
                   
                     ( 
                     2 
                     ) 
                   
                 
               
             
           
         
       
     
     For example, the range of timestamps may represent a range of valid timestamps (e.g., a range of 0-40,320 to represent the number of minutes in a 28-day time period) before a rollover occurs. In some such examples, the range of timestamps may be implemented by a range of timestamps based on Unix time. 
     In some examples, the timestamp generator circuitry  240  may determine the timestamp bitstream by determining a second value based on the second timestamp, the first value, and the range of timestamps based on the example of Equation (3) below: 
         L 5 VAL =timestamp minute −(timestamp range   *L 2 base ),   Equation (3)
 
     In some examples, the timestamp generator circuitry  240  may generate a first bit sequence to be inserted into a first encoding layer of a multilayer watermark based on the second value. For example, the timestamp generator circuitry  240  may determine L5 VAL  to correspond to the timestamp least significant bits  912  of  FIG.  9   . In some such examples, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may generate the first bit sequence by converting L5 VAL  into a binary value. In some such examples, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may encode the binary value into the fifth frequency layer  518  of the multilayer watermark  900 . In some such examples, L5 VAL  may correspond to a layer 5 value (L5 VAL ) to be used to determine the least significant bits of the timestamp bitstream. 
     In some examples, the timestamp generator circuitry  240  may determine the timestamp bitstream by determining a third value based on a sum of the first value and the second value based on the example of Equation (4) below: 
       PARITY=( L   2   BASE   +L 5 VAL ) &amp; 0x07F,   Equation (4)
 
     For example, the timestamp generator circuitry  240  may determine a parity value (PARITY), which may be converted to one or more parity bits, based on the sum of L2 BASE  and L5 VAL  shifted by an offset value (e.g., a hex value of 0x0F). Advantageously, in some such examples, the timestamp generator circuitry  240  may shift the sum by the hex value of 0x0F to ensure that an increment in the timestamp in minute format adjusts the least significant bits and the most significant bits of the timestamp bitstream, which may facilitate the error checking process. 
     In some examples, the timestamp generator circuitry  240  may determine the timestamp bitstream by generating a second bit sequence to be inserted into a second encoding layer of a multilayered watermark based on the first value and the parity bits based on the example of Equation (5) below: 
         L 3 VAL =( L   2   BASE *128)+PARITY,   Equation (5)
 
     For example, the timestamp generator circuitry  240  may determine L2 VAL  to correspond to the timestamp most significant bits and parity bits  914  of  FIG.  9   . In some such examples, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may generate the second bit sequence by converting L2 VAL  into a binary value. In some such examples, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may encode the binary value into the second frequency layer  514  of the multilayer watermark  900 . In some such examples, L2 VAL  may correspond to a layer 2 value (L2 VAL ) to be used to determine the most significant bits and the parity bits of the timestamp bitstream. 
     In some examples, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may encode the first bit sequence into the fifth frequency layer  518  and the second bit sequence into the second frequency layer  514 . In some examples, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260 , and/or, more generally, the watermark encoder  106 , may provide the encoded media to the media provider  102 , the AME  104 , and/or the media presentation device  112 . In some examples, the watermark decoders  124 ,  127  of  FIG.  1   , and/or, more generally, the first meter  120  and/or the second meter  126  of  FIG.  1   , may identify at least one of the first symbols  902 , the second symbols  904 , or the third symbols  906 . For example, the media identification determiner circuitry  330  of  FIG.  3    may identify the media identifier  910  in response to a detection of the first symbols  902  by the watermark detector circuitry  320  of  FIG.  3   . In some examples, the timestamp determiner circuitry  350  of  FIG.  3    may identify the most significant bits of the timestamp and the parity bits in response to a detection of the second symbols  904  by the watermark detector circuitry  320 . In some examples, the timestamp determiner circuitry  350  may identify the least significant bits of the timestamp in response to a detection of the third symbols  906  by the watermark detector circuitry  320 . In some examples, the timestamp determiner circuitry  350  may determine the timestamp based on the decoded ones of the most significant bits and the least significant bits. Advantageously, the timestamp determiner circuitry  350  may verify, validate, etc., an accuracy of the timestamp based on the parity bits. 
     Flowcharts representative of example hardware logic circuitry, machine readable instructions, hardware implemented state machines, and/or any combination thereof for implementing the watermark encoder  106  of  FIGS.  1  and/or  2   , the first watermark decoder  124  of  FIGS.  1  and/or  3   , the second watermark decoder  127  of  FIGS.  1  and/or  3   , and/or the AME  104  of  FIGS.  1  and/or  4    are shown in  FIGS.  10 - 13   . The machine readable instructions may be one or more executable programs or portion(s) of an executable program for execution by processor circuitry, such as the processor circuitry  1412  shown in the example processor platform  1400  discussed below in connection with  FIG.  14   , the processor circuitry  1512  shown in the example processor platform  1500  discussed below in connection with  FIG.  15   , the processor circuitry  1612  shown in the example processor platform  1600  discussed below in connection with  FIG.  16   , and/or the example processor circuitry discussed below in connection with  FIGS.  17  and/or  18   . The program may be embodied in software stored on one or more non-transitory computer readable storage media such as a CD, a floppy disk, an HDD, an SSD, a DVD, a Blu-ray disk, a volatile memory (e.g., Random Access Memory (RAM) of any type, etc.), or a non-volatile memory (e.g., electrically erasable programmable read-only memory (EEPROM), FLASH memory, an HDD, an SSD, etc.) associated with processor circuitry located in one or more hardware devices, but the entire program and/or parts thereof could alternatively be executed by one or more hardware devices other than the processor circuitry and/or embodied in firmware or dedicated hardware. The machine readable instructions may be distributed across multiple hardware devices and/or executed by two or more hardware devices (e.g., a server and a client hardware device). For example, the client hardware device may be implemented by an endpoint client hardware device (e.g., a hardware device associated with a user) or an intermediate client hardware device (e.g., a radio access network (RAN)) gateway that may facilitate communication between a server and an endpoint client hardware device). Similarly, the non-transitory computer readable storage media may include one or more mediums located in one or more hardware devices. Further, although the example program is described with reference to the flowcharts illustrated in  FIGS.  10 - 13   , many other methods of implementing the watermark encoder  106 , the first watermark decoder  124 , the second watermark decoder  127 , and/or the AME  104  may alternatively be used. For example, the order of execution of the blocks may be changed, and/or some of the blocks described may be changed, eliminated, or combined. Additionally or alternatively, any or all of the blocks may be implemented by one or more hardware circuits (e.g., processor circuitry, discrete and/or integrated analog and/or digital circuitry, an FPGA, an ASIC, a comparator, an operational-amplifier (op-amp), a logic circuit, etc.) structured to perform the corresponding operation without executing software or firmware. The processor circuitry may be distributed in different network locations and/or local to one or more hardware devices (e.g., a single-core processor (e.g., a single core central processor unit (CPU)), a multi-core processor (e.g., a multi-core CPU), etc.) in a single machine, multiple processors distributed across multiple servers of a server rack, multiple processors distributed across one or more server racks, a CPU and/or a FPGA located in the same package (e.g., the same integrated circuit (IC) package or in two or more separate housings, etc.). 
     The machine readable instructions described herein may be stored in one or more of a compressed format, an encrypted format, a fragmented format, a compiled format, an executable format, a packaged format, etc. Machine readable instructions as described herein may be stored as data or a data structure (e.g., as portions of instructions, code, representations of code, etc.) that may be utilized to create, manufacture, and/or produce machine executable instructions. For example, the machine readable instructions may be fragmented and stored on one or more storage devices and/or computing devices (e.g., servers) located at the same or different locations of a network or collection of networks (e.g., in the cloud, in edge devices, etc.). The machine readable instructions may require one or more of installation, modification, adaptation, updating, combining, supplementing, configuring, decryption, decompression, unpacking, distribution, reassignment, compilation, etc., in order to make them directly readable, interpretable, and/or executable by a computing device and/or other machine. For example, the machine readable instructions may be stored in multiple parts, which are individually compressed, encrypted, and/or stored on separate computing devices, wherein the parts when decrypted, decompressed, and/or combined form a set of machine executable instructions that implement one or more operations that may together form a program such as that described herein. 
     In another example, the machine readable instructions may be stored in a state in which they may be read by processor circuitry, but require addition of a library (e.g., a dynamic link library (DLL)), a software development kit (SDK), an application programming interface (API), etc., in order to execute the machine readable instructions on a particular computing device or other device. In another example, the machine readable instructions may need to be configured (e.g., settings stored, data input, network addresses recorded, etc.) before the machine readable instructions and/or the corresponding program(s) can be executed in whole or in part. Thus, machine readable media, as used herein, may include machine readable instructions and/or program(s) regardless of the particular format or state of the machine readable instructions and/or program(s) when stored or otherwise at rest or in transit. 
     The machine readable instructions described herein can be represented by any past, present, or future instruction language, scripting language, programming language, etc. For example, the machine readable instructions may be represented using any of the following languages: C, C++, Java, C#, Perl, Python, JavaScript, HyperText Markup Language (HTML), Structured Query Language (SQL), Swift, etc. 
     As mentioned above, the example operations of  FIGS.  10 - 13    may be implemented using executable instructions (e.g., computer and/or machine readable instructions) stored on one or more non-transitory computer and/or machine readable media such as optical storage devices, magnetic storage devices, an HDD, a flash memory, a read-only memory (ROM), a CD, a DVD, a cache, a RAM of any type, a register, and/or any other storage device or storage disk in which information is stored for any duration (e.g., for extended time periods, permanently, for brief instances, for temporarily buffering, and/or for caching of the information). As used herein, the terms non-transitory computer readable medium and non-transitory computer readable storage medium is expressly defined to include any type of computer readable storage device and/or storage disk and to exclude propagating signals and to exclude transmission media. 
     “Including” and “comprising” (and all forms and tenses thereof) are used herein to be open ended terms. Thus, whenever a claim employs any form of “include” or “comprise” (e.g., comprises, includes, comprising, including, having, etc.) as a preamble or within a claim recitation of any kind, it is to be understood that additional elements, terms, etc., may be present without falling outside the scope of the corresponding claim or recitation. As used herein, when the phrase “at least” is used as the transition term in, for example, a preamble of a claim, it is open-ended in the same manner as the term “comprising” and “including” are open ended. The term “and/or” when used, for example, in a form such as A, B, and/or C refers to any combination or subset of A, B, C such as (1) A alone, (2) B alone, (3) C alone, (4) A with B, (5) A with C, (6) B with C, or (7) A with B and with C. As used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. Similarly, as used herein in the context of describing structures, components, items, objects and/or things, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. As used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A and B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. Similarly, as used herein in the context of describing the performance or execution of processes, instructions, actions, activities and/or steps, the phrase “at least one of A or B” is intended to refer to implementations including any of (1) at least one A, (2) at least one B, or (3) at least one A and at least one B. 
     As used herein, singular references (e.g., “a”, “an”, “first”, “second”, etc.) do not exclude a plurality. The term “a” or “an” object, as used herein, refers to one or more of that object. The terms “a” (or “an”), “one or more”, and “at least one” are used interchangeably herein. Furthermore, although individually listed, a plurality of means, elements or method actions may be implemented by, e.g., the same entity or object. Additionally, although individual features may be included in different examples or claims, these may possibly be combined, and the inclusion in different examples or claims does not imply that a combination of features is not feasible and/or advantageous. 
       FIG.  10    is a flowchart representative of example machine readable instructions and/or example operations  1000  that may be executed and/or instantiated by processor circuitry to associate access of media and demographics of user(s) associated with device(s). The machine readable instructions and/or the operations  1000  of  FIG.  10    begin at block  1002 , at which the watermark encoder  106  ( FIG.  1   ) obtains media for watermark encoding. For example, the interface circuitry  210  ( FIG.  2   ) may obtain media from at least one of the media provider  102  ( FIG.  1   ) or the AME  104  ( FIG.  1   ). 
     At block  1004 , the watermark encoder  106  determines whether the media is scheduled to be accessed by device(s) after publishing of the media by a media provider. For example, the media identification generator circuitry  220  ( FIG.  2   ) may determine that the media is a linear program, RTVOD media, VOD media, etc., based on the media, or data associated with the media. 
     If, at block  1004 , the watermark encoder  106  determines that the media is not scheduled to be accessed by device(s) after publishing of the media by a media provider, then, at block  1006 , the watermark encoder  106  encodes the media with dense watermarks to indicate the media is accessed during a premiere of the media. For example, the dense watermark embedder circuitry  250  ( FIG.  2   ) may embed the media with the dense single layer watermark  600  of  FIG.  6   , the dense multilayer watermark  620  of  FIG.  6   , etc. In response to encoding the media with dense watermarks to indicate the media is accessed during a premier of the media at block  1006 , control proceeds to block  1010  to determine whether the encoded media is accessed by device(s). 
     If, at block  1004 , the watermark encoder  106  determines that the media is scheduled to be accessed by device(s) after publishing of the media by a media provider, control proceeds to block  1008  to encode the media with sparse watermarks to indicate the media is accessed within a time period after publishing of the media. For example, in response to a determination that the media is to be accessed within a first time period after the publishing of the media (e.g., within three days of the initial publishing of the media), the sparse watermark embedder circuitry  260  ( FIG.  2   ) may encode the media with the first sparse multilayer watermark  700  of  FIG.  7   . In some examples, in response to a determination that the media is to be accessed within a second time period after the publishing of the media (e.g., within seven days of the initial publishing of the media), the sparse watermark embedder circuitry  260  may encode the media with the second sparse multilayer watermark  730  of  FIG.  7   . An example process that may implement block  1008  is described below in connection with  FIG.  11   . 
     In response to encoding the media with sparse watermarks to indicate the media is accessed within a time period after publishing of the media at block  1008 , the watermark decoders  124 ,  127  ( FIG.  1   ) determine whether the encoded media is accessed by device(s) at block  1010 . For example, the watermark detector circuitry  320  ( FIG.  3   ) and/or the watermark detector circuitry  420  ( FIG.  4   ) may determine that the encoded media is accessed by the media presentation device  112  ( FIG.  1   ) in response to a detection of a watermark. 
     If, at block  1010 , the watermark decoders  124 ,  127  determine that the encoded media is not accessed by device(s), control proceeds to block  1022  to determine whether to continue monitoring for access of encoded media by device(s). If, at block  1010 , the watermark decoders  124 ,  127  determine that the encoded media is accessed by device(s), then, at block  1012 , the watermark decoders  124 ,  127  extract watermarks from audio of the encoded media. For example, the watermark detector circuitry  320  and/or the watermark detector circuitry  420  may extract the first sparse multilayer watermark  700  of  FIG.  7   , the second sparse multilayer watermark  730  of  FIG.  7   , etc., from audio output of the audio devices  132  ( FIG.  1   ). 
     At block  1014 , the watermark decoders  124 ,  127  identify symbol(s) at symbol position(s) of the watermark. For example, the watermark detector circuitry  320  and/or the watermark detector circuitry  420  may identify the first symbol  712  ( FIG.  7   ) at the first symbol position of the symbol positions  716  ( FIG.  7   ), the second symbol  714  ( FIG.  7   ) at the third symbol position of the symbol positions  716 , the third symbol  722  ( FIG.  7   ) at the fifth symbol position of the symbol positions  716 , and/or the fourth symbol  724  ( FIG.  7   ) at the eighth symbol position of the symbol positions  716 . 
     At block  1016 , the watermark decoders  124 ,  127  determine a time period associated with media access based on the symbol(s) at the symbol position(s). For example, the timestamp determiner circuitry  350  ( FIG.  3   ) and/or the timestamp determiner circuitry  450  ( FIG.  4   ) may determine that the media is accessed by the media presentation device  112  during a first time period in response to a detection of the first symbol  712  at the first symbol position, the second symbol  714  at the third symbol position, etc. In some such examples, the timestamp determiner circuitry  350  and/or the timestamp determiner circuitry  450  may determine that the detection of the first symbol  712  at the first symbol position, the second symbol  714  at the third symbol position, etc., indicates a first media state of the media (e.g., the media is accessed within three days of an initial publishing of the media by the media provider  102 ). 
     At block  1018 , the watermark decoders  124 ,  127  provide at least one of the media, the watermarks, or an indication of the time period to an audience measurement entity. For example, the interface circuitry  310  ( FIG.  3   ) may transmit at least one of the media, the first sparse multilayer watermark  700 , or the first media state to the AME  104  via the second network  110  ( FIG.  1   ). 
     At block  1020 , the AME  104  associates an access of the media and demographic(s) of user(s) associated with device(s). For example, the demographic associator circuitry  460  ( FIG.  4   ) may generate an association (e.g., a data association) of the access of the media by the media presentation device  112  and the demographic data  480  ( FIG.  4   ) that corresponds to a user (e.g., the panelist  116  ( FIG.  1   )) associated with the media presentation device  112 . In some such examples, the demographic associator circuitry  460  may store the association in the datastore  470  ( FIG.  4   ). In some examples, the demographic associator circuitry  460  may invoke the interface circuitry  410  to provide the association, the demographic data  480 , etc., to the media provider  102 . In some examples, the media provider  102  may improve a media platform (e.g., hardware, software, and/or firmware of the media platform) based on at least one of the association, the demographic data  480 , etc., because the at least one of the association, the demographic data  480 , etc., may indicate areas of improvement on how to access the media platform hosted by the media provider  102 . 
     At block  1022 , the watermark decoders  124 ,  127  determine whether to continue monitoring for access of encoded media by device(s). For example, the watermark detector circuitry  320  and/or the watermark detector circuitry  420  may determine whether another watermark is detected at the monitored site  130 . If, at block  1022 , the watermark decoders  124 ,  127  determine to continue monitoring for access of encoded media by device(s), control returns to block  1010  to determine whether encoded media is accessed by device(s), otherwise the example machine readable instructions and/or the operations  1000  of  FIG.  10    conclude. 
       FIG.  11    is a flowchart representative of example machine readable instructions and/or example operations  1100  that may be executed and/or instantiated by processor circuitry to encode media with sparse watermarks to indicate the media is accessed within a time period after publishing of the media. In some examples, the machine readable instructions and/or the operations  1100  of  FIG.  11    may be executed and/or instantiated by processor circuitry to implement block  1008  of  FIG.  10   . The machine readable instructions and/or the operations  1100  of  FIG.  11    begin at block  1102 , at which the watermark encoder  106  determines whether the media is scheduled to be accessed by device(s) within a first time period after publishing. For example, the media identification generator circuitry  220  ( FIG.  2   ) may determine that the media is to be accessed within three days after an initial publishing of the media by the media provider  102  ( FIG.  1   ). 
     If, at block  1102 , the watermark encoder  106  determines that the media is not scheduled to be accessed by device(s) within a first time period after publishing, control proceeds to block  1112  to determine whether the media is to be accessed by device(s) within a second time period after publishing. If, at block  1102 , the watermark encoder  106  determines that the media is scheduled to be accessed by device(s) within a first time period after publishing, then, at block  1104 , the watermark encoder  106  selects a first symbol to be inserted at a first symbol position on a first encoding layer of a multilayered watermark. For example, the sparse watermark embedder circuitry  260  ( FIG.  2   ) may select the first symbol  712  ( FIG.  7   ) to be inserted at the first symbol position of the symbol positions  716  ( FIG.  7   ) on the first layer  702  ( FIG.  7   ) of the first sparse multilayer watermark  700  ( FIG.  7   ). In some such examples, the sparse watermark embedder circuitry  260  may select the second symbol  714  ( FIG.  7   ) to be inserted at the third symbol position of the symbol positions  716  on the first layer  702  of the first sparse multilayer watermark  700 . 
     At block  1106 , the watermark encoder  106  selects a second symbol to be inserted at a second symbol position on a second encoding layer of the multilayered watermark. For example, the sparse watermark embedder circuitry  260  may select the third symbol  722  ( FIG.  7   ) to be inserted at the fifth symbol position of the symbol positions  716  on the second layer  704  of the first sparse multilayer watermark  700 . In some such examples, the sparse watermark embedder circuitry  260  may select the fourth symbol  724  ( FIG.  7   ) to be inserted at the eighth symbol position of the symbol positions  716  on the second layer  704  of the first sparse multilayer watermark  700 . 
     At block  1108 , the watermark encoder  106  encodes the first symbol in a media file at the first symbol position on the first encoding layer. For example, the sparse watermark embedder circuitry  260  may encode the first symbol  712  in the media at the first symbol position on the first layer  702 . In some such examples, the sparse watermark embedder circuitry  260  may encode the second symbol  714  in the media at the third symbol position on the first layer  702 . In some such examples, the sparse watermark embedder circuitry  260  may not include a symbol at the second, fourth, fifth, sixth, seventh, and/or eighth symbol position on the first layer  702 . 
     At block  1110 , the watermark encoder  106  encodes the second symbol in the media file at the second symbol position on the second encoding layer. For example, the sparse watermark embedder circuitry  260  may encode the third symbol  722  in the media at the fifth symbol position on the second layer  704 . In some such examples, the sparse watermark embedder circuitry  260  may encode the fourth symbol  724  in the media at the eighth symbol position on the second layer  704 . In some such examples, the sparse watermark embedder circuitry  260  may not include a symbol at the first, second, third, fourth, sixth, and/or seventh symbol position on the second layer  704 . 
     At block  1112 , the watermark encoder  106  determines whether the media is scheduled to be accessed by device(s) within a second time period after publishing. For example, the media identification generator circuitry  220  may determine that the media is to be accessed within seventh days after an initial publishing of the media by the media provider  102 . 
     If, at block  1112 , the watermark encoder  106  determines that the media is not scheduled to be accessed by device(s) within a second time period after publishing, control proceeds to block  1122  to determine whether to continue encoding the media file. If, at block  1112 , the watermark encoder  106  determines that the media is scheduled to be accessed by device(s) within a second time period after publishing, then, at block  1114 , the watermark encoder  106  selects a first symbol to be inserted at a third symbol position on a first encoding layer of a multilayered watermark. For example, the sparse watermark embedder circuitry  260  may select the fifth symbol  742  ( FIG.  7   ) to be inserted at the fourth symbol position of the symbol positions  716  on the first layer  702  of the second sparse multilayer watermark  730  ( FIG.  7   ). In some such examples, the sparse watermark embedder circuitry  260  may select the sixth symbol  744  ( FIG.  7   ) to be inserted at the seventh symbol position of the symbol positions  716  on the first layer  702  of the second sparse multilayer watermark  730 . 
     At block  1116 , the watermark encoder  106  selects a second symbol to be inserted at a fourth symbol position on a second encoding layer of the multilayered watermark. For example, the sparse watermark embedder circuitry  260  may select the seventh symbol  752  ( FIG.  7   ) to be inserted at the second symbol position of the symbol positions  716  on the second layer  704  of the second sparse multilayer watermark  730 . In some such examples, the sparse watermark embedder circuitry  260  may select the eighth symbol  754  ( FIG.  7   ) to be inserted at the sixth symbol position of the symbol positions  716  on the second layer  704  of the second sparse multilayer watermark  730 . 
     At block  1118 , the watermark encoder  106  encodes the first symbol in a media file at the third symbol position on the first encoding layer. For example, the sparse watermark embedder circuitry  260  may encode the fifth symbol  742  in the media at the fourth symbol position on the first layer  702 . In some such examples, the sparse watermark embedder circuitry  260  may encode the sixth symbol  744  in the media at the seventh symbol position on the first layer  702 . In some such examples, the sparse watermark embedder circuitry  260  may not include a symbol at the first, second, third, fifth, sixth, and/or seventh symbol position on the first layer  702 . 
     At block  1120 , the watermark encoder  106  encodes the second symbol in the media file at the fourth symbol position on the second encoding layer. For example, the sparse watermark embedder circuitry  260  may encode the seventh symbol  752  in the media at the second symbol position on the second layer  704 . In some such examples, the sparse watermark embedder circuitry  260  may encode the eighth symbol  754  in the media at the sixth symbol position on the second layer  704 . In some such examples, the sparse watermark embedder circuitry  260  may not include a symbol at the first, third, fourth, fifth, seventh, and/or eighth symbol position on the second layer  704   
     At block  1122 , the watermark encoder  106  determines whether to continue encoding the media file. For example, the media identification generator circuitry  220  ( FIG.  2   ) may determine that the encoding of the media file is complete, or portion(s) of the media file is/are yet to be encoded. If, at block  1122 , the watermark encoder  106  determines to continue encoding the media file, control returns to block  1102  to determine whether the media is scheduled to be accessed by device(s) within a first time period after publishing. If, at block  1122 , the watermark encoder  106  determines not to continue encoding the media file, the example machine readable instructions and/or the operations  1100  of  FIG.  11    conclude. For example, the machine readable instructions and/or the operations  1100  of  FIG.  11    may return to block  1010  of the machine readable instructions and/or the operations  1000  of  FIG.  10    to determine whether the encoded media is accessed by device(s). 
       FIG.  12    is a flowchart representative of example machine readable instructions and/or example operations  1200  that may be executed and/or instantiated by processor circuitry to associate demographics of user(s) with accessed media based on at least one of media identifiers or timestamps. The machine readable instructions and/or the operations  1200  of  FIG.  12    begin at block  1202 , at which the watermark encoder  106  ( FIG.  1   ) obtains media for watermark encoding. For example, the interface circuitry  210  ( FIG.  2   ) may obtain media from at least one of the media provider  102  ( FIG.  1   ) or the AME  104  ( FIG.  1   ). 
     At block  1204 , the watermark encoder  106  determines whether the media is scheduled to be accessed by device(s) after a premiere of the media. For example, the media identification generator circuitry  220  ( FIG.  2   ) may determine that the media is a linear program, RTVOD media, library VOD media, etc., based on the media, or data associated with the media. In some such examples, the media identification generator circuitry  220  may determine that the media is on-demand media, such as RTVOD or library VOD media, in response to a determination that the media is to be accessed after an initial publishing of the media on a media platform managed and/or otherwise hosted by the media provider  102 . 
     If, at block  1204 , the watermark encoder  106  determines that the media is not scheduled to be accessed by device(s) after a premiere of the media, then, at block  1206 , the watermark encoder  106  encodes the media with single layer watermarks to convey at least one of media identifiers (IDs) or timestamps. For example, the dense watermark embedder circuitry  250  ( FIG.  2   ) may embed the media with the single-layer watermark  800  ( FIG.  8   ) to convey at least one of the media identifier  805  ( FIG.  8   ) or the timestamp  810  ( FIG.  8   ). In response to encoding the media with single layer watermarks to convey at least one of media IDs or timestamps at block  1206 , control proceeds to block  1210  to determine whether the encoded media is accessed by device(s). 
     If, at block  1204 , the watermark encoder  106  determines that the media is scheduled to be accessed by device(s) after a premiere of the media, control proceeds to block  1208  to encode the media with multilayer watermarks to convey at least one of media IDs or timestamps. An example process that may implement block  1208  is described below in connection with  FIG.  13   . In response to encoding the media with multilayer watermarks to convey at least one of media IDs or timestamps at block  1208 , the watermark decoders  124 ,  127  ( FIG.  1   ) determines whether the encoded media is accessed by device(s) at block  1210 . For example, the watermark detector circuitry  320  ( FIG.  3   ) and/or the watermark detector circuitry  420  ( FIG.  4   ) may determine that the encoded media is accessed by the media presentation device  112  ( FIG.  1   ) in response to a detection of a watermark. 
     If, at block  1210 , the watermark decoders  124 ,  127  determine that the encoded media is not accessed by device(s), control proceeds to block  1220  to determine whether to continue monitoring for access of encoded media by device(s). If, at block  1210 , the watermark decoders  124 ,  127  determine that the encoded media is accessed by device(s), then, at block  1212 , the watermark decoders  124 ,  127  extract watermarks from audio of the encoded media. For example, the watermark detector circuitry  320  may extract the multilayer watermark  900  of  FIG.  9    from audio output of the audio devices  132  ( FIG.  1   ). 
     At block  1214 , the watermark decoders  124 ,  127  identify at least one of media IDs or timestamps based on the extracted watermarks. For example, the watermark detector circuitry  320  and/or the watermark detector circuitry  420  may identify the first symbols  902  ( FIG.  9   ) on at least one of the second frequency layer  514  ( FIG.  5   ) or the fifth frequency layer  518  ( FIG.  5   ). In some such examples, the media identification determiner circuitry  330  ( FIG.  3   ) and/or the media identification determiner circuitry  430  ( FIG.  4   ) may identify the media identifier  910  based on the first symbols  902 . In some examples, the watermark detector circuitry  320  and/or the watermark detector circuitry  420  may identify the second symbols  904  on the second frequency layer  514  and/or the third symbols  906  on the fifth frequency layer  518 . In some such examples, the timestamp determiner circuitry  350  ( FIG.  3   ) and/or the timestamp determiner circuitry  450  ( FIG.  4   ) may identify the timestamp most significant bits and the parity bits  914  based on the second symbols  904  and the timestamp least significant bits  912  based on the third symbols  906 . In some such examples, the timestamp determiner circuitry  350  and/or the timestamp determiner circuitry  450  may identify the timestamp based on a combination, aggregation, etc., of the most significant bits and the least significant bits. 
     At block  1216 , the watermark decoders  124 ,  127  provide at least one of media identifiers or timestamps to an audience measurement entity. For example, the interface circuitry  310  ( FIG.  3   ) may transmit at least one of the media identifier  910  or the timestamp based on the timestamp least significant bits  912  and the timestamp most significant bits  914  to the AME  104  via the second network  110  ( FIG.  1   ). 
     At block  1218 , the AME  104  associates demographics of user(s) with the accessed media based on the at least one of the media IDs or the timestamps. For example, the demographic associator circuitry  460  ( FIG.  4   ) may generate an association (e.g., a data association) of the access of the media by the media presentation device  112  and the demographic data  480  ( FIG.  4   ) that corresponds to a user (e.g., the panelist  116  ( FIG.  1   )) associated with the media presentation device  112 . In some such examples, the demographic associator circuitry  460  may store the association in the datastore  470  ( FIG.  4   ). In some examples, the demographic associator circuitry  460  may invoke the interface circuitry  410  to provide the association, the demographic data  480 , etc., to the media provider  102 . 
     At block  1220 , the watermark decoders  124 ,  127  determine whether to continue monitoring for access of encoded media by device(s). For example, the watermark detector circuitry  320  and/or the watermark detector circuitry  420  may determine whether another watermark is detected at the monitored site  130 . If, at block  1220 , the watermark decoders  124 ,  127  determine to continue monitoring for access of encoded media by device(s), control returns to block  1210  to determine whether encoded media is accessed by device(s), otherwise the example machine readable instructions and/or the operations  1200  of  FIG.  12    conclude. 
       FIG.  13    is a flowchart representative of example machine readable instructions and/or example operations  1300  that may be executed and/or instantiated by processor circuitry to encode media with multilayer watermarks to convey at least one of media identifiers or timestamps. The machine readable instructions and/or the operations  1300  of  FIG.  13    begin at block  1302 , at which the watermark encoder  106  converts a first timestamp in time second format to a second timestamp in time minute format. For example, the timestamp generator circuitry  240  ( FIG.  2   ) may determine timestamp minute  based on the example of Equation (1) above. 
     At block  1304 , the watermark encoder  106  determines a first value based on the second timestamp and a range of timestamps. For example, the timestamp generator circuitry  240  may determine L2 BASE  based on the example of Equation (2) above. 
     At block  1306 , the watermark encoder  106  may determine a second value based on the second timestamp, the first value, and the range of timestamps. For example, the timestamp generator circuitry  240  may determine L5 VAL  based on the example of Equation (3) above. 
     At block  1308 , the watermark encoder  106  may generate a first bit sequence to be inserted into a first encoding layer of a multilayered watermark based on the second value. For example, the timestamp generator circuitry  240  may convert L5 VAL  into a first bit sequence that includes the timestamp least significant bits  912  ( FIG.  9   ). In some such examples, at least one of the dense watermark embedder circuitry  250  ( FIG.  2   ) or the sparse watermark embedder circuitry  260  ( FIG.  2   ) may generate the third symbols  906  ( FIG.  9   ) based on the timestamp least significant bits  912 . 
     At block  1310 , the watermark encoder  106  determines a third value based on a sum of the first value and the second value. For example, the timestamp generator circuitry  240  may determine the third value based on a sum of L2 BASE  and L5 VAL . 
     At block  1312 , the watermark encoder  106  determines parity bits based on an offset of a converted bit stream of the third value. For example, the timestamp generator circuitry  240  may convert the third value into a bit stream. In some such examples, the timestamp generator circuitry  240  may determine the parity bits based on an offset of the bit stream by an offset value. For example, the timestamp generator circuitry  240  may determine the parity bits based on the example of Equation (4) above. 
     At block  1314 , the watermark encoder  106  generates a second bit sequence to be inserted into a second encoding layer of the multilayered watermark based on the first value and the parity bits. For example, the timestamp generator circuitry  240  may generate L2 VAL  based on the example of Equation (5) above. In some such examples, the at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may generate the second symbols  904  ( FIG.  9   ) based on the timestamp most significant bits and parity bits  914  ( FIG.  9   ). 
     At block  1316 , the watermark encoder  106  encodes the first bit sequence in media on the first encoding layer of the multilayered watermark. For example, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may encode the third symbols  906  on the fifth frequency layer  518  of the multilayered watermark  900  ( FIG.  9   ). 
     At block  1318 , the watermark encoder  106  encodes the second bit sequence in the media on the second encoding layer of the multilayered watermark. For example, at least one of the dense watermark embedder circuitry  250  or the sparse watermark embedder circuitry  260  may encode the second symbols  904  on the second frequency layer  514  of the multilayered watermark  900 . 
     In response to encoding the second bit sequence in the media on the second encoding layer of the multilayered watermark at block  1318 , the example machine readable instructions and/or the operations  1300  of  FIG.  13    conclude. For example, the machine readable instructions and/or the operations  1300  of  FIG.  13    may return to block  1210  of the machine readable instructions and/or the operations  1200  of  FIG.  12    to determine whether the encoded media is accessed by device(s). 
       FIG.  14    is a block diagram of an example processor platform  1400  structured to execute and/or instantiate the machine readable instructions and/or the operations of  FIGS.  10 ,  11 ,  12   , and/or  13  to implement the watermark encoder  106  of  FIGS.  1  and/or  2   . The processor platform  1400  can be, for example, a server, a personal computer, a workstation, a self-learning machine (e.g., a neural network), a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), or any other type of computing device. 
     The processor platform  1400  of the illustrated example includes processor circuitry  1412 . The processor circuitry  1412  of the illustrated example is hardware. For example, the processor circuitry  1412  can be implemented by one or more integrated circuits, logic circuits, FPGAs microprocessors, CPUs, GPUs, DSPs, and/or microcontrollers from any desired family or manufacturer. The processor circuitry  1412  may be implemented by one or more semiconductor based (e.g., silicon based) devices. In this example, the processor circuitry  1412  implements the media identification generator circuitry  220  (identified by MEDIA ID GENERATOR CIRCUITRY), the source identification generator circuitry  230  (identified by SOURCE ID GENERATOR CIRCUITRY), the timestamp generator circuitry  240 , the dense watermark embedder circuitry  250  (identified by DENSE WM EMBEDDER CIRCUITRY), and the sparse watermark embedder circuitry  260  (identified by SPARSE WM EMBEDDER CIRCUITRY) of  FIG.  2   . 
     The processor circuitry  1412  of the illustrated example includes a local memory  1413  (e.g., a cache, registers, etc.). The processor circuitry  1412  of the illustrated example is in communication with a main memory including a volatile memory  1414  and a non-volatile memory  1416  by a bus  1418 . In some examples, the bus  1418  may implement the bus  280  of  FIG.  2   . The volatile memory  1414  may be implemented by Synchronous Dynamic Random Access Memory (SDRAM), Dynamic Random Access Memory (DRAM), RAIVIBUS® Dynamic Random Access Memory (RDRAM®), and/or any other type of RAM device. The non-volatile memory  1416  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1414 ,  1416  of the illustrated example is controlled by a memory controller  1417 . 
     The processor platform  1400  of the illustrated example also includes interface circuitry  1420 . The interface circuitry  1420  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a USB interface, a Bluetooth® interface, an NFC interface, a PCI interface, and/or a PCIe interface. In this example, the interface circuitry  1420  implements the interface circuitry  210  of  FIG.  2   . 
     In the illustrated example, one or more input devices  1422  are connected to the interface circuitry  1420 . The input device(s)  1422  permit(s) a user to enter data and/or commands into the processor circuitry  1412 . The input device(s)  1422  can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, an isopoint device, and/or a voice recognition system. 
     One or more output devices  1424  are also connected to the interface circuitry  1420  of the illustrated example. The output device(s)  1424  can be implemented, for example, by display devices (e.g., a light emitting diode (LED), an organic light emitting diode (OLED), a liquid crystal display (LCD), a cathode ray tube (CRT) display, an in-place switching (IPS) display, a touchscreen, etc.), a tactile output device, a printer, and/or speaker. The interface circuitry  1420  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip, and/or graphics processor circuitry such as a GPU. 
     The interface circuitry  1420  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem, a residential gateway, a wireless access point, and/or a network interface to facilitate exchange of data with external machines (e.g., computing devices of any kind) by a network  1426 . In some examples, the network  1426  may implement the first network  108  of  FIG.  1   . The communication can be by, for example, an Ethernet connection, a digital subscriber line (DSL) connection, a telephone line connection, a coaxial cable system, a satellite system, a line-of-site wireless system, a cellular telephone system, an optical connection, etc. 
     The processor platform  1400  of the illustrated example also includes one or more mass storage devices  1428  to store software and/or data. Examples of such mass storage devices  1428  include magnetic storage devices, optical storage devices, floppy disk drives, HDDs, CDs, Blu-ray disk drives, redundant array of independent disks (RAID) systems, solid state storage devices such as flash memory devices and/or SSDs, and DVD drives. In this example, the one or more mass storage devices  1428  implement the datastore  270  of  FIG.  2   , which includes the media  272 , the identifiers  274 , the timestamps  276 , and the watermarks  278  of  FIG.  2   . 
     The machine executable instructions  1432 , which may be implemented by the machine readable instructions of  FIGS.  10 ,  11 ,  12   , and/or  13 , may be stored in the mass storage device  1428 , in the volatile memory  1414 , in the non-volatile memory  1416 , and/or on a removable non-transitory computer readable storage medium such as a CD or DVD. 
       FIG.  15    is a block diagram of an example processor platform  1500  structured to execute and/or instantiate the machine readable instructions and/or the operations of  FIGS.  10  and/or  12    to implement the first watermark decoder  124  of  FIGS.  1  and/or  3    and/or the second watermark decoder  127  of  FIGS.  1  and/or  3   . The processor platform  1500  can be, for example, a server, a personal computer, a workstation, a self-learning machine (e.g., a neural network), a mobile device (e.g., a cell phone, a smart phone, a tablet such as an iPad™), a personal digital assistant (PDA), an Internet appliance, a DVD player, a CD player, a digital video recorder, a Blu-ray player, a gaming console, a personal video recorder, a set top box, a headset (e.g., an augmented reality (AR) headset, a virtual reality (VR) headset, etc.) or other wearable device, or any other type of computing device. 
     The processor platform  1500  of the illustrated example includes processor circuitry  1512 . The processor circuitry  1512  of the illustrated example is hardware. For example, the processor circuitry  1512  can be implemented by one or more integrated circuits, logic circuits, FPGAs microprocessors, CPUs, GPUs, DSPs, and/or microcontrollers from any desired family or manufacturer. The processor circuitry  1512  may be implemented by one or more semiconductor based (e.g., silicon based) devices. In this example, the processor circuitry  1512  implements the watermark detector circuitry  320 , the media identification determiner circuitry  330  (identified by MEDIA ID DETERMINER CIRCUITRY), the source identification determiner circuitry  340  (identified by SOURCE ID DETERMINER CIRCUITRY), and the timestamp determiner circuitry  350  of  FIG.  3   . 
     The processor circuitry  1512  of the illustrated example includes a local memory  1513  (e.g., a cache, registers, etc.). The processor circuitry  1512  of the illustrated example is in communication with a main memory including a volatile memory  1514  and a non-volatile memory  1516  by a bus  1518 . In some examples, the bus  1518  may implement the bus  380  of  FIG.  3   . The volatile memory  1514  may be implemented by SDRAM, DRAM, RDRAM®, and/or any other type of RAM device. The non-volatile memory  1516  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1514 ,  1516  of the illustrated example is controlled by a memory controller  1517 . 
     The processor platform  1500  of the illustrated example also includes interface circuitry  1520 . The interface circuitry  1520  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a USB interface, a Bluetooth® interface, an NFC interface, a PCI interface, and/or a PCIe interface. In this example, the interface circuitry  1520  implements the interface circuitry  310  of  FIG.  3   . 
     In the illustrated example, one or more input devices  1522  are connected to the interface circuitry  1520 . The input device(s)  1522  permit(s) a user to enter data and/or commands into the processor circuitry  1512 . The input device(s)  1522  can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, an isopoint device, and/or a voice recognition system. 
     One or more output devices  1524  are also connected to the interface circuitry  1520  of the illustrated example. The output device(s)  1524  can be implemented, for example, by display devices (e.g., an LED, an OLED, an LCD, a CRT display, an IPS display, a touchscreen, etc.), a tactile output device, a printer, and/or speaker. The interface circuitry  1520  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip, and/or graphics processor circuitry such as a GPU. 
     The interface circuitry  1520  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem, a residential gateway, a wireless access point, and/or a network interface to facilitate exchange of data with external machines (e.g., computing devices of any kind) by a network  1526 . In some examples, the network  1526  may implement the second network  110  of  FIG.  1   . The communication can be by, for example, an Ethernet connection, a DSL connection, a telephone line connection, a coaxial cable system, a satellite system, a line-of-site wireless system, a cellular telephone system, an optical connection, etc. 
     The processor platform  1500  of the illustrated example also includes one or more mass storage devices  1528  to store software and/or data. Examples of such mass storage devices  1528  include magnetic storage devices, optical storage devices, floppy disk drives, HDDs, CDs, Blu-ray disk drives, RAID systems, solid state storage devices such as flash memory devices and/or SSDs, and DVD drives. In this example, the one or more mass storage devices  1528  implements the datastore  370  of  FIG.  3   , which includes the identifiers  374 , the timestamps  376 , and the watermarks  378  of  FIG.  3   . 
     The machine executable instructions  1532 , which may be implemented by the machine readable instructions of  FIGS.  10  and/or  12   , may be stored in the mass storage device  1528 , in the volatile memory  1514 , in the non-volatile memoryl 516 , and/or on a removable non-transitory computer readable storage medium such as a CD or DVD. 
       FIG.  16    is a block diagram of an example processor platform  1600  structured to execute and/or instantiate the machine readable instructions and/or the operations of  FIGS.  10  and/or  12    to implement the AME  104  of  FIGS.  1  and/or  4   . The processor platform  1600  can be, for example, a server, a personal computer, a workstation, a self-learning machine (e.g., a neural network), or any other type of computing device. 
     The processor platform  1600  of the illustrated example includes processor circuitry  1612 . The processor circuitry  1612  of the illustrated example is hardware. For example, the processor circuitry  1612  can be implemented by one or more integrated circuits, logic circuits, FPGAs microprocessors, CPUs, GPUs, DSPs, and/or microcontrollers from any desired family or manufacturer. The processor circuitry  1612  may be implemented by one or more semiconductor based (e.g., silicon based) devices. In this example, the processor circuitry  1612  implements the watermark detector circuitry  420 , the media identification determiner circuitry  430  (identified by MEDIA ID DETERMINER CIRCUITRY), the source identification determiner circuitry  440  (identified by SOURCE ID DETERMINER CIRCUITRY), the timestamp determiner circuitry  450 , and the demographic associator circuitry  460  of  FIG.  4   . 
     The processor circuitry  1612  of the illustrated example includes a local memory  1613  (e.g., a cache, registers, etc.). The processor circuitry  1612  of the illustrated example is in communication with a main memory including a volatile memory  1614  and a non-volatile memory  1616  by a bus  1618 . In some examples, the bus  1618  may implement the bus  490  of  FIG.  4   . The volatile memory  1614  may be implemented by SDRAM, DRAM, RDRAM®, and/or any other type of RAM device. The non-volatile memory  1616  may be implemented by flash memory and/or any other desired type of memory device. Access to the main memory  1614 ,  1616  of the illustrated example is controlled by a memory controller  1617 . 
     The processor platform  1600  of the illustrated example also includes interface circuitry  1620 . The interface circuitry  1620  may be implemented by hardware in accordance with any type of interface standard, such as an Ethernet interface, a USB interface, a Bluetooth® interface, an NFC interface, a PCI interface, and/or a PCIe interface. In this example, the interface circuitry  1620  implements the interface circuitry  410  of  FIG.  4   . 
     In the illustrated example, one or more input devices  1622  are connected to the interface circuitry  1620 . The input device(s)  1622  permit(s) a user to enter data and/or commands into the processor circuitry  1612 . The input device(s)  1622  can be implemented by, for example, an audio sensor, a microphone, a camera (still or video), a keyboard, a button, a mouse, a touchscreen, a track-pad, a trackball, an isopoint device, and/or a voice recognition system. 
     One or more output devices  1624  are also connected to the interface circuitry  1620  of the illustrated example. The output device(s)  1624  can be implemented, for example, by display devices (e.g., an LED, an OLED, an LCD, a CRT display, an IPS display, a touchscreen, etc.), a tactile output device, a printer, and/or speaker. The interface circuitry  1620  of the illustrated example, thus, typically includes a graphics driver card, a graphics driver chip, and/or graphics processor circuitry such as a GPU. 
     The interface circuitry  1620  of the illustrated example also includes a communication device such as a transmitter, a receiver, a transceiver, a modem, a residential gateway, a wireless access point, and/or a network interface to facilitate exchange of data with external machines (e.g., computing devices of any kind) by a network  1626 . In some examples, the network  1626  may implement the first network  108  and/or the second network  110  of  FIG.  1   . The communication can be by, for example, an Ethernet connection, a DSL connection, a telephone line connection, a coaxial cable system, a satellite system, a line-of-site wireless system, a cellular telephone system, an optical connection, etc. 
     The processor platform  1600  of the illustrated example also includes one or more mass storage devices  1628  to store software and/or data. Examples of such mass storage devices  1628  include magnetic storage devices, optical storage devices, floppy disk drives, HDDs, CDs, Blu-ray disk drives, RAID systems, solid state storage devices such as flash memory devices and/or SSDs, and DVD drives. In this example, the one or more mass storage devices  1628  implements the datastore  470  of  FIG.  4   , which includes the media  472 , the identifiers  474 , the timestamps  476 , the watermarks  478 , and the demographic data  480  of  FIG.  4   . 
     The machine executable instructions  1632 , which may be implemented by the machine readable instructions of  FIGS.  10  and/or  12   , may be stored in the mass storage device  1628 , in the volatile memory  1614 , in the non-volatile memory  1616 , and/or on a removable non-transitory computer readable storage medium such as a CD or DVD. 
       FIG.  17    is a block diagram of an example implementation of the processor circuitry  1412  of  FIG.  4   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16   . In this example, the processor circuitry  1412  of  FIG.  4   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16    is implemented by a general purpose microprocessor  1700 . The general purpose microprocessor circuitry  1700  execute some or all of the machine readable instructions of the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13  to effectively instantiate the watermark encoder  106  of  FIGS.  1  and/or  2   , the first watermark decoder  124  of  FIGS.  1  and/or  3   , the second watermark decoder  127  of  FIGS.  1  and/or  3   , and/or the AME of  FIGS.  1  and/or  4    as logic circuits to perform the operations corresponding to those machine readable instructions. For example, the microprocessor  1700  may implement multi-core hardware circuitry such as a CPU, a DSP, a GPU, an XPU, etc. Although it may include any number of example cores  1702  (e.g., 1 core), the microprocessor  1700  of this example is a multi-core semiconductor device including N cores. The cores  1702  of the microprocessor  1700  may operate independently or may cooperate to execute machine readable instructions. For example, machine code corresponding to a firmware program, an embedded software program, or a software program may be executed by one of the cores  1702  or may be executed by multiple ones of the cores  1702  at the same or different times. In some examples, the machine code corresponding to the firmware program, the embedded software program, or the software program is split into threads and executed in parallel by two or more of the cores  1702 . The software program may correspond to a portion or all of the machine readable instructions and/or operations represented by the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13 . 
     The cores  1702  may communicate by a first example bus  1704 . In some examples, the first bus  1704  may implement a communication bus to effectuate communication associated with one(s) of the cores  1702 . For example, the first bus  1704  may implement at least one of an I2C bus, a SPI bus, a PCI bus, or a PCIe bus. Additionally or alternatively, the first bus  1704  may implement any other type of computing or electrical bus. 
     The cores  1702  may obtain data, instructions, and/or signals from one or more external devices by example interface circuitry  1706 . The cores  1702  may output data, instructions, and/or signals to the one or more external devices by the interface circuitry  1706 . Although the cores  1702  of this example include example local memory  1720  (e.g., Level 1 (L1) cache that may be split into an L1 data cache and an L1 instruction cache), the microprocessor  1700  also includes example shared memory  1710  that may be shared by the cores (e.g., Level 2 (L2_cache)) for high-speed access to data and/or instructions. Data and/or instructions may be transferred (e.g., shared) by writing to and/or reading from the shared memory  1710 . The local memory  1720  of each of the cores  1702  and the shared memory  1710  may be part of a hierarchy of storage devices including multiple levels of cache memory and the main memory (e.g., the main memory  1414 ,  1416  of  FIG.  14   , the main memory  1514 ,  1516  of  FIG.  15   , and/or the main memory  1614 ,  1616  of  FIG.  16   ). Typically, higher levels of memory in the hierarchy exhibit lower access time and have smaller storage capacity than lower levels of memory. Changes in the various levels of the cache hierarchy are managed (e.g., coordinated) by a cache coherency policy. 
     Each core  1702  may be referred to as a CPU, DSP, GPU, etc., or any other type of hardware circuitry. Each core  1702  includes control unit circuitry  1714 , arithmetic and logic (AL) circuitry (sometimes referred to as an ALU)  1716 , a plurality of registers  1718 , the L1 cache  1720 , and a second example bus  1722 . Other structures may be present. For example, each core  1702  may include vector unit circuitry, single instruction multiple data (SIMD) unit circuitry, load/store unit (LSU) circuitry, branch/jump unit circuitry, floating-point unit (FPU) circuitry, etc. The control unit circuitry  1714  includes semiconductor-based circuits structured to control (e.g., coordinate) data movement within the corresponding core  1702 . The AL circuitry  1716  includes semiconductor-based circuits structured to perform one or more mathematic and/or logic operations on the data within the corresponding core  1702 . The AL circuitry  1716  of some examples performs integer based operations. In other examples, the AL circuitry  1716  also performs floating point operations. In yet other examples, the AL circuitry  1716  may include first AL circuitry that performs integer based operations and second AL circuitry that performs floating point operations. In some examples, the AL circuitry  1716  may be referred to as an Arithmetic Logic Unit (ALU). The registers  1718  are semiconductor-based structures to store data and/or instructions such as results of one or more of the operations performed by the AL circuitry  1716  of the corresponding core  1702 . For example, the registers  1718  may include vector register(s), SIMD register(s), general purpose register(s), flag register(s), segment register(s), machine specific register(s), instruction pointer register(s), control register(s), debug register(s), memory management register(s), machine check register(s), etc. The registers  1718  may be arranged in a bank as shown in  FIG.  17   . Alternatively, the registers  1718  may be organized in any other arrangement, format, or structure including distributed throughout the core  1702  to shorten access time. The second bus  1722  may implement at least one of an I2C bus, a SPI bus, a PCI bus, or a PCIe bus 
     Each core  1702  and/or, more generally, the microprocessor  1700  may include additional and/or alternate structures to those shown and described above. For example, one or more clock circuits, one or more power supplies, one or more power gates, one or more cache home agents (CHAs), one or more converged/common mesh stops (CMSs), one or more shifters (e.g., barrel shifter(s)) and/or other circuitry may be present. The microprocessor  1700  is a semiconductor device fabricated to include many transistors interconnected to implement the structures described above in one or more integrated circuits (ICs) contained in one or more packages. The processor circuitry may include and/or cooperate with one or more accelerators. In some examples, accelerators are implemented by logic circuitry to perform certain tasks more quickly and/or efficiently than can be done by a general purpose processor. Examples of accelerators include ASICs and FPGAs such as those discussed herein. A GPU or other programmable device can also be an accelerator. Accelerators may be on-board the processor circuitry, in the same chip package as the processor circuitry and/or in one or more separate packages from the processor circuitry. 
       FIG.  18    is a block diagram of another example implementation of the processor circuitry  1412  of  FIG.  14   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16   . In this example, the processor circuitry  1412  of  FIG.  14   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16    is implemented by FPGA circuitry  1800 . The FPGA circuitry  1800  can be used, for example, to perform operations that could otherwise be performed by the example microprocessor  1700  of  FIG.  17    executing corresponding machine readable instructions. However, once configured, the FPGA circuitry  1800  instantiates the machine readable instructions in hardware and, thus, can often execute the operations faster than they could be performed by a general purpose microprocessor executing the corresponding software. 
     More specifically, in contrast to the microprocessor  1700  of  FIG.  17    described above (which is a general purpose device that may be programmed to execute some or all of the machine readable instructions represented by the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13  but whose interconnections and logic circuitry are fixed once fabricated), the FPGA circuitry  1800  of the example of  FIG.  18    includes interconnections and logic circuitry that may be configured and/or interconnected in different ways after fabrication to instantiate, for example, some or all of the machine readable instructions represented by the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13 . In particular, the FPGA  1800  may be thought of as an array of logic gates, interconnections, and switches. The switches can be programmed to change how the logic gates are interconnected by the interconnections, effectively forming one or more dedicated logic circuits (unless and until the FPGA circuitry  1800  is reprogrammed). The configured logic circuits enable the logic gates to cooperate in different ways to perform different operations on data received by input circuitry. Those operations may correspond to some or all of the software represented by the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13 . As such, the FPGA circuitry  1800  may be structured to effectively instantiate some or all of the machine readable instructions of the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13  as dedicated logic circuits to perform the operations corresponding to those software instructions in a dedicated manner analogous to an ASIC. Therefore, the FPGA circuitry  1800  may perform the operations corresponding to the some or all of the machine readable instructions of  FIGS.  10 ,  11 ,  12   , and/or  13  faster than the general purpose microprocessor can execute the same. 
     In the example of  FIG.  18   , the FPGA circuitry  1800  is structured to be programmed (and/or reprogrammed one or more times) by an end user by a hardware description language (HDL) such as Verilog. The FPGA circuitry  1800  of  FIG.  18   , includes example input/output (I/O) circuitry  1802  to obtain and/or output data to/from example configuration circuitry  1804  and/or external hardware (e.g., external hardware circuitry)  1806 . For example, the configuration circuitry  1804  may implement interface circuitry that may obtain machine readable instructions to configure the FPGA circuitry  1800 , or portion(s) thereof. In some such examples, the configuration circuitry  1804  may obtain the machine readable instructions from a user, a machine (e.g., hardware circuitry (e.g., programmed or dedicated circuitry) that may implement an Artificial Intelligence/Machine Learning (AI/ML) model to generate the instructions), etc. In some examples, the external hardware  1806  may implement the microprocessor  1700  of  FIG.  17   . The FPGA circuitry  1800  also includes an array of example logic gate circuitry  1808 , a plurality of example configurable interconnections  1810 , and example storage circuitry  1812 . The logic gate circuitry  1808  and interconnections  1810  are configurable to instantiate one or more operations that may correspond to at least some of the machine readable instructions of  FIGS.  10 ,  11 ,  12   , and/or  13  and/or other desired operations. The logic gate circuitryl 808  shown in  FIG.  18    is fabricated in groups or blocks. Each block includes semiconductor-based electrical structures that may be configured into logic circuits. In some examples, the electrical structures include logic gates (e.g., And gates, Or gates, Nor gates, etc.) that provide basic building blocks for logic circuits. Electrically controllable switches (e.g., transistors) are present within each of the logic gate circuitry  1808  to enable configuration of the electrical structures and/or the logic gates to form circuits to perform desired operations. The logic gate circuitry  1808  may include other electrical structures such as look-up tables (LUTs), registers (e.g., flip-flops or latches), multiplexers, etc. 
     The interconnections  1810  of the illustrated example are conductive pathways, traces, vias, or the like that may include electrically controllable switches (e.g., transistors) whose state can be changed by programming (e.g., using an HDL instruction language) to activate or deactivate one or more connections between one or more of the logic gate circuitry  1808  to program desired logic circuits. 
     The storage circuitry  1812  of the illustrated example is structured to store result(s) of the one or more of the operations performed by corresponding logic gates. The storage circuitry  1812  may be implemented by registers or the like. In the illustrated example, the storage circuitry  1812  is distributed amongst the logic gate circuitry  1808  to facilitate access and increase execution speed. 
     The example FPGA circuitry  1800  of  FIG.  18    also includes example Dedicated Operations Circuitry  1814 . In this example, the Dedicated Operations Circuitry  1814  includes special purpose circuitry  1816  that may be invoked to implement commonly used functions to avoid the need to program those functions in the field. Examples of such special purpose circuitry  1816  include memory (e.g., DRAM) controller circuitry, PCIe controller circuitry, clock circuitry, transceiver circuitry, memory, and multiplier-accumulator circuitry. Other types of special purpose circuitry may be present. In some examples, the FPGA circuitry  1800  may also include example general purpose programmable circuitry  1818  such as an example CPU  1820  and/or an example DSP  1822 . Other general purpose programmable circuitry  1818  may additionally or alternatively be present such as a GPU, an XPU, etc., that can be programmed to perform other operations. 
     Although  FIGS.  17  and  18    illustrate two example implementations of the processor circuitry  1412  of  FIG.  14   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16   , many other approaches are contemplated. For example, as mentioned above, modern FPGA circuitry may include an on-board CPU, such as one or more of the example CPU  1820  of  FIG.  18   . Therefore, the processor circuitry  1412  of  FIG.  14   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16    may additionally be implemented by combining the example microprocessor  1700  of  FIG.  17    and the example FPGA circuitry  1800  of  FIG.  18   . In some such hybrid examples, a first portion of the machine readable instructions represented by the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13  may be executed by one or more of the cores  1702  of  FIG.  17    and a second portion of the machine readable instructions represented by the flowcharts of  FIGS.  10 ,  11 ,  12   , and/or  13  may be executed by the FPGA circuitry  1800  of  FIG.  18   . 
     In some examples, the processor circuitry  1412  of  FIG.  14   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16    may be in one or more packages. For example, the processor circuitry  1700  of  FIG.  17    and/or the FPGA circuitry  1800  of  FIG.  18    may be in one or more packages. In some examples, an XPU may be implemented by the processor circuitry  1412  of  FIG.  14   , the processor circuitry  1512  of  FIG.  15   , and/or the processor circuitry  1612  of  FIG.  16   , which may be in one or more packages. For example, the XPU may include a CPU in one package, a DSP in another package, a GPU in yet another package, and an FPGA in still yet another package. 
     A block diagram illustrating an example software distribution platform  1605  to distribute software such as the example machine readable instructions  1432  of  FIG.  14   , the example machine readable instructions  1532  of  FIG.  15   , and the example machine readable instructions  1632  of  FIG.  16    to hardware devices owned and/or operated by third parties is illustrated in  FIG.  19   . The example software distribution platform  1905  may be implemented by any computer server, data facility, cloud service, etc., capable of storing and transmitting software to other computing devices. The third parties may be customers of the entity owning and/or operating the software distribution platform  1905 . For example, the entity that owns and/or operates the software distribution platform  1905  may be a developer, a seller, and/or a licensor of software such as the example machine readable instructions  1432  of  FIG.  14   , the example machine readable instructions  1532  of  FIG.  15   , and the example machine readable instructions  1632  of  FIG.  16   . The third parties may be consumers, users, retailers, OEMs, etc., who purchase and/or license the software for use and/or re-sale and/or sub-licensing. In the illustrated example, the software distribution platform  1905  includes one or more servers and one or more storage devices. The storage devices store the machine readable instructions  1432 ,  1532 ,  1632 , which may correspond to the example machine readable instructions  1000 ,  1100 ,  1200 ,  1300  of  FIGS.  10 - 13   , as described above. The one or more servers of the example software distribution platform  1905  are in communication with a network  1910 , which may correspond to any one or more of the Internet and/or any of the example networks  108 ,  110 ,  1426 ,  1526 ,  1626  described above. In some examples, the one or more servers are responsive to requests to transmit the software to a requesting party as part of a commercial transaction. Payment for the delivery, sale, and/or license of the software may be handled by the one or more servers of the software distribution platform and/or by a third party payment entity. The servers enable purchasers and/or licensors to download the machine readable instructions  1432 ,  1532 ,  1632  from the software distribution platform  1905 . For example, the software, which may correspond to the example machine readable instructions  1000 ,  1100 ,  1200 ,  1300  of  FIGS.  10 - 13   , may be downloaded to the example processor platform  1400 , which is to execute the machine readable instructions  1432  to implement the watermark encoder  106  of  FIGS.  1  and/or  2   . In some examples, the software may be downloaded to the example processor platform  1500 , which is to execute the machine readable instructions  1532  to implement the first watermark decoder  124  of  FIGS.  1  and/or  3    and/or the second watermark decoder  127  of  FIGS.  1  and/or  3   . In some examples, the software may be downloaded to the example processor platform  1600 , which is to execute the machine readable instructions to implement the AME  104  of  FIGS.  1  and/or  4   . In some example, one or more servers of the software distribution platform  1905  periodically offer, transmit, and/or force updates to the software (e.g., the example machine readable instructions  1432 ,  1532 ,  1632  of  FIGS.  14 - 16   ) to ensure improvements, patches, updates, etc., are distributed and applied to the software at the end user devices. 
     From the foregoing, it will be appreciated that example systems, methods, apparatus, and articles of manufacture have been disclosed that improve watermark detection in acoustic environments. Disclosed systems, methods, apparatus, and articles of manufacture improve the efficiency of using a computing device by adding hardware, software, and/or firmware to detect sparse watermarks as disclosed herein. Disclosed systems, methods, apparatus, and articles of manufacture improve the efficiency of using a computing device by adding hardware, software, and/or firmware to detect timestamps in multilayer watermarks as disclosed herein. Disclosed systems, methods, apparatus, and articles of manufacture are accordingly directed to one or more improvement(s) in the operation of a machine such as a computer or other electronic and/or mechanical device. 
     Example methods, apparatus, systems, and articles of manufacture to improve watermark detection in acoustic environments are disclosed herein. Further examples and combinations thereof include the following: 
     Example 1 includes an apparatus comprising at least one memory, instructions in the apparatus, and processor circuitry to execute and/or instantiate the instructions to encode a first symbol in a media file at a first symbol position on a first encoding layer of a multilayered watermark, and encode a second symbol in the media file at a second symbol position on a second encoding layer of the multilayered watermark, the first encoding layer and the second encoding layer including a plurality of symbol positions, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     Example 2 includes the apparatus of example 1, wherein the processor circuitry is to execute and/or instantiate the instructions to identify the media file as scheduled to be accessed by a media device after a publishing of the media file by a media provider, and in response to identifying the media file as scheduled to be accessed by the media device within a first time period after the publishing of the media file, select the first symbol to be inserted at the first symbol position and the second symbol to be inserted at the second symbol position to identify an access of the media filed by the media device within the first time period. 
     Example 3 includes the apparatus of example 2, wherein the processor circuitry is to execute and/or instantiate the instructions to in response to identifying the media file as scheduled to be accessed by the media device within a second time period after the publishing of the media file select the first symbol to be inserted at a third symbol position on the first encoding layer and the second symbol to be inserted at a fourth symbol position on the second encoding layer, encode the first symbol in the media file at the third symbol position on the first encoding layer, and encode the second symbol in the media file at the fourth symbol position on the second encoding layer, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     Example 4 includes the apparatus of example 3, wherein the first time period is within three days after the publishing of the media file and the second time period is within seven days after the publishing of the media file. 
     Example 5 includes the apparatus of example 2, wherein the publishing of the media file includes a television broadcast of the media file or availability of the media file on a streaming media platform. 
     Example 6 includes the apparatus of example 1, wherein the processor circuitry is to execute and/or instantiate the instructions to in response to an access of the media file by a media device, extract the multilayered watermark from audio of the media file, identify the first symbol at the first symbol position and the second symbol at the second symbol position, determine that the media file is accessed within a first time period or a second time period after a publishing of the media file by a media provider based on the first symbol at the first symbol position and the second symbol at the second symbol position, and provide an indication to a server that the media file is accessed within the first time period or the second time period. 
     Example 7 includes the apparatus of example 6, wherein the processor circuitry is to execute and/or instantiate the instructions to associate the access of the media file and demographics of a user associated with the meter based on the indication. 
     Example 8 includes at least one non-transitory computer readable storage medium comprising instructions that, when executed, cause processor circuitry to at least encode a first symbol in a media file at a first symbol position on a first encoding layer of a multilayered watermark, and encode a second symbol in the media file at a second symbol position on a second encoding layer of the multilayered watermark, the first encoding layer and the second encoding layer including a plurality of symbol positions, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     Example 9 includes the at least one non-transitory computer readable storage medium of example 8, wherein the instructions, when executed, cause the processor circuitry to identify the media file as scheduled to be accessed by a media device after a publishing of the media file by a media provider, and in response to identifying the media file as scheduled to be accessed by the media device within a first time period after the publishing of the media file, select the first symbol to be inserted at the first symbol position and the second symbol to be inserted at the second symbol position to identify an access of the media filed by the media device within the first time period. 
     Example 10 includes the at least one non-transitory computer readable storage medium of example 9, wherein the instructions, when executed, cause the processor circuitry to in response to identifying the media file as scheduled to be accessed by the media device within a second time period after the publishing of the media file select the first symbol to be inserted at a third symbol position on the first encoding layer and the second symbol to be inserted at a fourth symbol position on the second encoding layer, encode the first symbol in the media file at the third symbol position on the first encoding layer, and encode the second symbol in the media file at the fourth symbol position on the second encoding layer, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     Example 11 includes the at least one non-transitory computer readable storage medium of example 10, wherein the first time period is within three days after the publishing of the media file and the second time period is within seven days after the publishing of the media file. 
     Example 12 includes the at least one non-transitory computer readable storage medium of example 9, wherein the publishing of the media file includes a television broadcast of the media file or availability of the media file on a streaming media platform. 
     Example 13 includes the at least one non-transitory computer readable storage medium of example 8, wherein the instructions, when executed, cause the processor circuitry to in response to an access of the media file by a media device, extract the multilayered watermark from audio of the media file, identify the first symbol at the first symbol position and the second symbol at the second symbol position, determine that the media file is accessed within a first time period or a second time period after a publishing of the media file by a media provider based on the first symbol at the first symbol position and the second symbol at the second symbol position, and provide an indication to a server that the media file is accessed within the first time period or the second time period. 
     Example 14 includes the at least one non-transitory computer readable storage medium of example 13, wherein the instructions, when executed, cause the processor circuitry to associate the access of the media file and demographics of a user associated with the meter based on the indication. 
     Example 15 includes a method comprising encoding a first symbol in a media file at a first symbol position on a first encoding layer of a multilayered watermark, and encoding a second symbol in the media file at a second symbol position on a second encoding layer of the multilayered watermark, the first encoding layer and the second encoding layer including a plurality of symbol positions, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     Example 16 includes the method of example 15, further including identifying the media file as scheduled to be accessed by a media device after a publishing of the media file by a media provider, and in response to identifying the media file as scheduled to be accessed by the media device within a first time period after the publishing of the media file, selecting the first symbol to be inserted at the first symbol position and the second symbol to be inserted at the second symbol position to identify an access of the media filed by the media device within the first time period. 
     Example 17 includes the method of example 16, further including in response to identifying the media file as scheduled to be accessed by the media device within a second time period after the publishing of the media file selecting the first symbol to be inserted at a third symbol position on the first encoding layer and the second symbol to be inserted at a fourth symbol position on the second encoding layer, encoding the first symbol in the media file at the third symbol position on the first encoding layer, and encoding the second symbol in the media file at the fourth symbol position on the second encoding layer, one or more of the plurality of the symbol positions on at least one of the first encoding layer or the second encoding layer to be empty. 
     Example 18 includes the method of example 17, wherein the first time period is within three days after the publishing of the media file and the second time period is within seven days after the publishing of the media file. 
     Example 19 includes the method of example 16, wherein the publishing of the media file includes a television broadcast of the media file or availability of the media file on a streaming media platform. 
     Example 20 includes the method of example 15, further including in response to an access of the media file by a media device, extracting, with a meter, the multilayered watermark from audio of the media file, identifying, with the meter, the first symbol at the first symbol position and the second symbol at the second symbol position, determining, with the meter, that the media file is accessed within a first time period or a second time period after a publishing of the media file by a media provider based on the first symbol at the first symbol position and the second symbol at the second symbol position, and providing an indication to a server that the media file is accessed within the first time period or the second time period. 
     Example 21 includes the method of example 20, further including associating the access of the media file and demographics of a user associated with the meter based on the indication. 
     Example 22 includes an apparatus comprising at least one memory, instructions in the apparatus, and processor circuitry to execute and/or instantiate the instructions to encode a first bit sequence in a media file on a first encoding layer of a multilayered watermark, the first bit sequence to include one or more first bits associated with a timestamp of the multilayered watermark, and encode a second bit sequence in the media file on a second encoding layer of the multilayered watermark, the second bit sequence to include (i) one or more second bits associated with the timestamp and (ii) one or more third bits. 
     Example 23 includes the apparatus of example 22, wherein the one or more third bits are parity bits. 
     Example 24 includes the apparatus of example 22, wherein the processor circuitry is to execute and/or instantiate the instructions to convert the timestamp in a first format to a second format, the first format based on a number of seconds at which the multilayered watermark is to be encoded in the media file, the second format based on a number of minutes at which the multilayered watermark is to be encoded in the media file, and convert the timestamp in the second format to a third bit sequence, the first bit sequence corresponding to one or more least significant bits of the third bit sequence, the second bit sequence corresponding to one or more most significant bits of the third bit sequence. 
     Example 25 includes the apparatus of example 22, wherein the processor circuitry is to execute and/or instantiate the instructions to determine a first value based on the timestamp and a range of timestamps, determine a second value based on the timestamp, the first value, and the range of timestamps, and convert the second value into the first bit sequence. 
     Example 26 includes the apparatus of example 25, wherein the processor circuitry is to execute and/or instantiate the instructions to determine a third value based on a sum of the first value and the second value, convert the third value into a third bit sequence, and determine the one or more third bits by shifting the third bit sequence by an offset value. 
     Example 27 includes the apparatus of example 26, wherein the media file is to be encoded with a plurality of multilayered watermarks with associated timestamps, successive ones of the timestamps to be incremented at a minute level, the plurality of the multilayered watermarks including the multilayer watermark, the timestamps including the timestamp, and the processor circuitry is to execute and/or instantiate the instructions to increment successive ones of the plurality of the timestamps at the minute level, and in response to the incrementing of the successive ones of the plurality of the timestamps, increment the first bit sequence and the second bit sequence of respective ones of the successive ones of the plurality of the timestamps. 
     Example 28 includes the apparatus of example 25, wherein the processor circuitry is to execute and/or instantiate the instructions to determine a third value based on a multiplication of the first value and a fourth value, determine a fifth value based on a sum of the third value and a parity value, the parity value to be converted into the one or more third bits, and convert the fifth value into the one or more second bits. 
     Example 29 includes at least one non-transitory computer readable storage medium comprising instructions that, when executed, cause processor circuitry to at least encode a first bit sequence in a media file on a first encoding layer of a multilayered watermark, the first bit sequence to include one or more first bits associated with a timestamp of the multilayered watermark, and encode a second bit sequence in the media file on a second encoding layer of the multilayered watermark, the second bit sequence to include (i) one or more second bits associated with the timestamp and (ii) one or more third bits. 
     Example 30 includes the at least one non-transitory computer readable storage medium of example 29, wherein the one or more third bits are parity bits. 
     Example 31 includes the at least one non-transitory computer readable storage medium of example 29, wherein the instructions, when executed, cause the processor circuitry to convert the timestamp in a first format to a second format, the first format based on a number of seconds at which the multilayered watermark is to be encoded in the media file, the second format based on a number of minutes at which the multilayered watermark is to be encoded in the media file, and convert the timestamp in the second format to a third bit sequence, the first bit sequence corresponding to one or more least significant bits of the third bit sequence, the second bit sequence corresponding to one or more most significant bits of the third bit sequence. 
     Example 32 includes the at least one non-transitory computer readable storage medium of example 29, wherein the instructions, when executed, cause the processor circuitry to determine a first value based on the timestamp and a range of timestamps, determine a second value based on the timestamp, the first value, and the range of timestamps, and convert the second value into the first bit sequence. 
     Example 33 includes the at least one non-transitory computer readable storage medium of example 32, wherein the instructions, when executed, cause the processor circuitry to determine a third value based on a sum of the first value and the second value, convert the third value into a third bit sequence, and determine the one or more third bits by shifting the third bit sequence by an offset value. 
     Example 34 includes the at least one non-transitory computer readable storage medium of example 33, wherein the media file is to be encoded with a plurality of multilayered watermarks with associated timestamps, successive ones of the timestamps to be incremented at a minute level, the plurality of the multilayered watermarks including the multilayer watermark, the timestamps including the timestamp, and the instructions, when executed, cause the processor circuitry to increment successive ones of the plurality of the timestamps at the minute level, and in response to the incrementing of the successive ones of the plurality of the timestamps, increment the first bit sequence and the second bit sequence of respective ones of the successive ones of the plurality of the timestamps. 
     Example 35 includes the at least one non-transitory computer readable storage medium of example 32, wherein the instructions, when executed, cause the processor circuitry to determine a third value based on a multiplication of the first value and a fourth value, determine a fifth value based on a sum of the third value and a parity value, the parity value to be converted into the one or more third bits, and convert the fifth value into the one or more second bits. 
     Example 36 includes a method comprising encoding a first bit sequence in a media file on a first encoding layer of a multilayered watermark, the first bit sequence to include one or more first bits associated with a timestamp of the multilayered watermark, and encoding a second bit sequence in the media file on a second encoding layer of the multilayered watermark, the second bit sequence to include (i) one or more second bits associated with the timestamp and (ii) one or more third bits. 
     Example 37 includes the method of example 36, wherein the one or more third bits are parity bits. 
     Example 38 includes the method of example 36, further including converting the timestamp in a first format to a second format, the first format based on a number of seconds at which the multilayered watermark is to be encoded in the media file, the second format based on a number of minutes at which the multilayered watermark is to be encoded in the media file, and converting the timestamp in the second format to a third bit sequence, the first bit sequence corresponding to one or more least significant bits of the third bit sequence, the second bit sequence corresponding to one or more most significant bits of the third bit sequence. 
     Example 39 includes the method of example 36, further including determining a first value based on the timestamp and a range of timestamps, determining a second value based on the timestamp, the first value, and the range of timestamps, and converting the second value into the first bit sequence. 
     Example 40 includes the method of example 39, further including determining a third value based on a sum of the first value and the second value, converting the third value into a third bit sequence, and determining the one or more third bits by shifting the third bit sequence by an offset value. 
     Example 41 includes the method of example 40, wherein the media file is to be encoded with a plurality of multilayered watermarks with associated timestamps, successive ones of the timestamps to be incremented at a minute level, the plurality of the multilayered watermarks including the multilayer watermark, the timestamps including the timestamp, and further including incrementing successive ones of the plurality of the timestamps at the minute level, and in response to the incrementing of the successive ones of the plurality of the timestamps, incrementing the first bit sequence and the second bit sequence of respective ones of the successive ones of the plurality of the timestamps. 
     Example 42 includes the method of example 39, further including determining a third value based on a multiplication of the first value and a fourth value, determining a fifth value based on a sum of the third value and a parity value, the parity value to be converted into the one or more third bits, and converting the fifth value into the one or more second bits. 
     The following claims are hereby incorporated into this Detailed Description by this reference. Although certain example systems, methods, apparatus, and articles of manufacture have been disclosed herein, the scope of coverage of this patent is not limited thereto. On the contrary, this patent covers all systems, methods, apparatus, and articles of manufacture fairly falling within the scope of the claims of this patent.