Patent Publication Number: US-2015071615-A1

Title: Video Display Control Using Embedded Metadata

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation of U.S. patent application Ser. No. 13/580,051 filed Aug. 20, 2012, which is a National Phase entry of PCT Patent Application Serial No. PCT/US2011/025185, having international filing date of Feb. 17, 2011, which claims priority to U.S. Provisional Patent Application No. 61/306,900, filed Feb. 22, 2010. The contents of all of the above applications are incorporated by reference in their entirety for all purposes. 
    
    
     TECHNICAL FIELD 
     This invention relates to systems, apparatus and methods for delivering video data and/or controlling display of video data. Some embodiments provide systems, apparatus and methods for delivering other data in a stream of video data. Some embodiments provide systems, apparatus and methods for generating, delivering, processing and displaying video data to preserve the video creator=s creative intent. 
     BACKGROUND 
       FIG. 1  is a flowchart of a conventional video delivery pipeline  100  showing various stages from video capture to video content display. A sequence of video frames  101  is captured at block  102 . Video frames  101  may be digitally captured (e.g. by a digital camera) or generated by a computer (e.g. using computer animation) to provide a stream of video data  103 . Alternately, video frames  101  may be captured on film by a film camera. The film is converted to a digital format to provide a stream of video data  103 . 
     Video data  103  is provided to a processor at block  104  for post-production editing. Block  104  post-production editing may include adjusting or modifying colors or brightness in particular areas of an image to enhance the image quality or achieve a particular appearance for the image in accordance with the video creator=s creative intent. Other editing (e.g. scene selection and sequencing, image cropping, addition of computer-generated visual special effects, etc.) may be performed at block  104 . During block  104  post-production editing, video images are viewed on a reference display. 
     Following post-production, video data  103  is delivered at block  106  to a display subsystem. As seen in  FIG. 1A , block  106  delivery includes an encoder stage  107 A for driving broadcast or transmission of video data  103  over a video distribution medium  105  (e.g. satellite, cable, DVD, etc). A decoder stage  107 B is located at the display end of block  106  to decode video data  103  transmitted over medium  105 . The display subsystem may include a video processor and a display. At block  108 , video data  103  is provided to the video processor for processing and/or decoding. Video data  103  is output to the display at block  110  to display a sequence of images to a viewer. 
     To improve the quality of the displayed images, video data  103  may be driven through video delivery pipeline  100  at a relatively high bit rate so as to facilitate an increased bit depth for defining RGB or chroma values for each chrominance (color) channel. For example, a stream of video data  103  may comprise 8, 10 or 12 bits of data for each chrominance channel of a pixel. 
     Despite using a high bit depth for each chrominance channel, variations in display characteristics (such as luminance range, gamut, etc.) may affect the appearance of an image rendered on a display so that the image rendered does not match the creative intent of the video=s creator. In particular, the perceived color or brightness of an image rendered on a particular display subsystem may differ from the color or brightness of the image as viewed on the reference display during block  104  post-production editing. 
     Moreover, methods applied at processing or display stages of a conventional video delivery pipeline, such as those stages represented by blocks  104 ,  108  and  110  of video delivery pipeline  100  ( FIG. 1 ), are typically performed in a pre-configured manner without taking into account processing which may have occurred at other stages of video delivery pipeline  100 . For example, the block  110  methods for displaying video data  103  may be performed without knowledge of how prior processing steps in video delivery pipeline  100  were carried out, such as block  104  post-production editing. The block  110  display methods may not be suitable for rendering an image on the display in a manner which preserves the video creator=s creative intent, as determined by block  104  post-production editing. 
     There is a general desire for systems, apparatus and methods for generating, delivering, processing and displaying video data to preserve the video creator=s creative intent. There is a general desire for systems, apparatus and methods for providing information which may be used to guide downstream processing and/or display of video data. 
     SUMMARY 
     Systems, apparatus and methods are provided for providing video data including metadata to a display subsystem. The video data may be transmitted or provided to the display subsystem using systems, apparatus and methods suitable for the type of content delivery (e.g. television broadcast over satellite, cable, or high-definition networks; streaming multimedia over IP or wireless networks; playback from DVD or other storage media, etc.). In particular embodiments, metadata is generated and embedded in the video data at one or more stages of a video delivery pipeline. The metadata may provide information relating to: characteristics of a reference display used to edit the video data, characteristics of the environment in which the reference display is situated, characteristics of the edited image (e.g. luminance and gamut), characteristics of the viewing environment in which the display of the display subsystem is situated, etc. 
     The metadata is delivered with the video data to downstream apparatus such as a display subsystem. The metadata may be delivered and received by the downstream apparatus in advance of a video frame for which the embedded metadata is to be applied. The metadata may be extracted and decoded at the display subsystem and applied to configure a display of the display subsystem and/or to process the video data to adjust the video data for the display. 
     In certain embodiments, the metadata may be embedded in the video data by overwriting a plurality of guard bits in the video data. In other embodiments, the metadata may be embedded in the video data by overwriting a plurality of least significant bits in the video data, such as least significant bits of chrominance channels. Other types of data may be embedded in the video data using the methods described herein. 
     Methods of encoding the metadata are provided so as to avoid unintentional communication of reserved video words (e.g. reserved pixel values) and/or reserved metadata words (e.g. start or end of frame headers). In embodiments where the guard bits are overwritten with metadata, the plurality of video data bits preceding a guard bit may be compared to reserved video words to determine whether the guard bit should contain a guard; otherwise, a bit of metadata may be embedded in the guard bit. 
     In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed descriptions. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
       Exemplary embodiments are illustrated in referenced figures of the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
         FIG. 1  is a flowchart illustrating the stages of a conventional video delivery pipeline. 
         FIG. 1A  is a flowchart illustrating the stages of delivery of video data that may be performed in the  FIG. 1  video delivery pipeline. 
         FIG. 2A  illustrates frames of video data in visual-dynamic range (VDR) format, having guard bits which may be used to carry metadata according to particular embodiments. 
         FIG. 2B  illustrates frames of video data in non-VDR formats, having least significant bits in each chrominance channel which may be used to carry metadata according to particular embodiments. 
         FIG. 2C  illustrates frames of video data in non-VDR formats, having groups of bits which may be used to carry metadata according to particular embodiments. 
         FIG. 3  is a flowchart illustrating the flow of video data through a video delivery pipeline and a method of generating, delivering, processing and displaying video data according to one embodiment to preserve the video creator=s creative intent. 
         FIG. 3A  is a flowchart illustrating the stages of delivery of video data that may be performed in the  FIG. 3  video delivery pipeline. 
         FIG. 4A  is a flowchart showing a method according to one embodiment of encoding metadata in video data. 
         FIG. 4B  is a flowchart showing a method according to one embodiment of decoding metadata that has been encoded in video data using the method of  FIG. 4A . 
         FIGS. 5A and 5B  are flowcharts showing methods of encoding metadata in video data according to other particular embodiments. 
         FIG. 6A  shows a metadata packet according to one embodiment. 
         FIG. 6B  shows a header that may be used to frame the metadata packet of  FIG. 6A . 
         FIG. 7  shows metadata that may be delivered for a sequence of frames, and a timeline illustrating when the received metadata is to be applied. 
         FIG. 8  is a flowchart showing a method of managing delivery of metadata according to one embodiment. 
         FIG. 9  schematically depicts a system according to one embodiment which may be used to implement one or more of the methods described herein. 
         FIG. 10  shows a sequence of metadata packets containing different types of metadata transmitted over two consecutive video frames. 
         FIG. 11A  schematically depicts a subsystem according to one embodiment that may be used to encode metadata in video data. 
         FIG. 11B  schematically depicts a subsystem according to one embodiment that may be used to extract metadata from video data. 
     
    
    
     DESCRIPTION 
     Throughout the following description, specific details are set forth in order to provide a more thorough understanding to persons skilled in the art. However, well known elements may not have been shown or described in detail to avoid unnecessarily obscuring the disclosure. Accordingly, the description and drawings are to be regarded in an illustrative, rather than a restrictive, sense. 
     Example embodiments provide for systems, apparatus and methods useful in a video delivery pipeline. Metadata is written in video data and transmitted with the video data through the video delivery pipeline. The metadata may, for example, be useful for guiding downstream devices in processing video data and/or guiding video playback on a display. The display may be a flat panel display (e.g. LCD, LED, OLED, high-dynamic range, or plasma display) such as may be provided in a television, computer monitor, laptop, cellular phone or handheld mobile device, and the like, or any other display capable of displaying video data. 
     Metadata may be dynamically generated and written or embedded in the video data stream at various stages throughout the video delivery pipeline including video capture, post-production editing, and pre-display processing. The metadata may define parameters, including, for example: gamut and other characteristics of a reference display used in post-production editing, location of light sources in an image, protected colors of an image which should not be altered, etc. Such metadata may be decoded and processed by a decoder and/or a display and used for processing of video data and/or display management and configuration to control and enhance video playback on the display. Metadata may be used to control a display (and/or process video data for the display) to display video in a manner which preserves the video creator=s creative intent. 
     According to particular embodiments, video data may include guard bits and/or least significant bits (LSBs) such as LSBs of chrominance channels. In some embodiments, metadata is carried in the guard bits and/or LSBs. For video formats such as VDR format (see  FIG. 2A ), a video data frame  10  may include one or more guard bits  11 . Metadata  225  may be written in at least some of the guard bits  11 . For other video formats such as a non-VDR format (see  FIG. 2B ), a video data frame  10  may include one or more LSBs  12  (e.g. LSBs  12  in each of the chrominance or luminance channels). Metadata  225  may be written in at least some of the LSBs  12 . The Human Vision System (HVS) tends to be less sensitive to changes in chromaticity than changes in luminance. Therefore, given this HVS characteristic, in some embodiments metadata  225  may be written in an LSB  12  in one or more of the chrominance channels. Bits of metadata  225  may be serialized onto guard bits  11  and/or LSBs  12  within video data frames  10  to provide packets of metadata  225  of variable or fixed length. VDR format is a video format described in co-owned PCT Application No. PCT/US2010/022700 for AEXTENDED DYNAMIC RANGE AND EXTENDED DIMENSIONALITY IMAGE SIGNAL CONVERSION AND/OR DELIVERY VIA LEGACY VIDEO INTERFACES @ which is herein incorporated by reference. 
     For video data in non-VDR or other formats having LSBs (e.g. LSBs of chrominance channels), metadata may be written in the LSBs in one of the following ways, for example:
         Metadata may be written in the LSB of each chrominance channel, such that all LSBs potentially carry metadata.   Metadata may be written in round-robin fashion in the LSB of each chrominance channel or in some other manner which skips some LSBs, so that not all LSBs potentially carry metadata.   Metadata may be written in LSBs of chrominance channels of pixels in areas of the image which have a relatively reduced tendency to be affected by overwriting the LSBs. For example, in some embodiments, metadata may be written in the LSBs of chrominance channels of pixels in brighter image areas to take advantage of the general tendency that changes in the displayed image caused by overwriting the LSB are less noticeable in brighter image areas.
 
In certain embodiments, a method of writing metadata in LSBs may be selected to account for a possible loss of image quality in video content display which may result from overwriting the LSB of each chrominance channel (or other types of data) to carry metadata. Methods of writing metadata may be selected based on the video data or image so as to reduce or minimize artifacts in the displayed image.
       

     As a variable amount of metadata may be transmitted through the video delivery pipeline for each video frame, methods and apparatus may be provided to manage the timing of delivery and processing of the metadata. For example, a metadata payload spanning a plurality of video frames may be transmitted to and received by a video decoder or processor in advance of processing of the particular video frame at which the metadata is to be applied. The metadata payload may be sent with a timestamp indicating when the metadata is to be applied by the video decoder or processor to manage or configure the display. 
     A metadata payload may be assigned a priority level. Systems, apparatus and/or methods may be provided so that metadata categorized as relatively higher priority metadata may be delivered prior to delivery of metadata categorized as relatively lower priority metadata. Such systems, apparatus and/or methods may be used to manage metadata delivery where there is insufficient bandwidth in the video delivery pipeline to transmit all of the metadata generated for one or more video frames. In particular embodiments, transmittal of certain metadata through the video delivery pipeline may be temporarily interrupted to allow transmittal of other metadata categorized as relatively higher priority metadata. 
     Other transport mechanisms may be provided to carry additional metadata. For example, in some video formats, video data includes chrominance data which is represented separately from luminance data. Some embodiments provide bursts of metadata through the video delivery pipeline, by overwriting chrominance data for particular video frames or areas of video frames with metadata. For pixels for which the luminance level is zero or below a threshold value, chrominance data may be overwritten with bits of metadata  225  without substantially affecting the appearance of the displayed image. Metadata may be written in chrominance portions or chrominance channels of video data which may include fields, values, bits, etc.  FIG. 2C  shows chrominance portions comprising series of bits  13  in data frames  10 , which may be overwritten with metadata  225 . Encoding of metadata in chrominance portions is described in a co-owned, co-pending application entitled SYSTEMS, APPARATUS AND METHODS FOR VIDEO DELIVERY AND CONTROLLING VIDEO DISPLAY BY OVERWRITING VIDEO DATA, which is incorporated herein by reference. 
       FIG. 3  is a flowchart showing the flow of data through a video delivery pipeline  200  according to a particular embodiment. Video delivery pipeline  200  incorporates similar stages as those depicted in video delivery pipeline  100  of  FIG. 1 , and accordingly, similar reference numerals are used to identify the similar stages, except that in video delivery pipeline  200  of  FIG. 3 , the reference numerals begin with a A2@ instead of a A1@. At one or more stages of video delivery pipeline  200 , metadata  225  may be generated and embedded in a stream of video data  203  for use at a downstream stage. Metadata  225  is transmitted along with video data  203  through video delivery pipeline  200  to guide downstream devices in processing the video data and/or to guide video playback at a display subsystem at block  210 . Video data  203 , including embedded metadata  225 , may be delivered to the display subsystem at block  206  using systems, apparatus and methods suitable for the type of video content delivery (e.g. television broadcast over satellite, cable, or high-definition networks; streaming multimedia over IP or wireless networks; playback from DVD or other storage media, etc.). 
     In the  FIG. 3  embodiment, camera metadata  225 A is generated and embedded in video data  203  at block  202 . Camera metadata  225 A may be generated based on the camera settings and video frame capture environment. Camera metadata  225 A may comprise, for example, camera parameters which provide a snapshot of the camera settings during video frame capture. Such camera parameters may include aperture (f-stops), lens, shutter speed, sensitivity (ISO ratings) and the like. These camera parameters may be used to guide subsequent steps in video delivery pipeline  200 , such as color adjustments (e.g. color timing) during post-production editing at block  204 , or display configuration at block  210 . 
     At block  204 , post-production metadata  225 B is generated and embedded in video data  203 . Post-production metadata  225 B may include: reference display and environment metadata  225 B 1  and source video content characterization metadata  225 B 2 . Post-production metadata  225 B may be used to guide subsequent steps in video delivery pipeline  200 , such as display configuration at block  210 . 
     Reference display and environment metadata  225 B 1  may describe the reference display configuration and studio or viewing environment used in the block  204  post-production editing. For example, with respect to the reference display used to display video data  203  during the block  204  post-production editing, reference display and environment metadata  225 B 1  may include parameters such as:
         a 3D color gamut mapping describing the tone and gamut boundaries of the reference display at a detailed resolution;   a reduced set of parameters defining the tone and gamut boundaries of the reference display (which may be used to estimate a 3D color gamut mapping);   system tonal response parameters describing the tonal response of the reference display for each chrominance channel;   and/or the like.       

     Reference display and environment metadata  225 B 1  may also include parameters describing the studio environment in which video content was color-timed or edited on a reference display during the block  204  post-production editing. Such parameters may include ambient luminance and ambient color temperature. 
     Source video content characterization metadata  225 B 2  may describe post-production edited video content including information which may identify or provide:
         a location map of light sources in an image, or of reflective or emissive objects in an image;   gamut of the video source content;   areas of an image which are color-timed purposely out of gamut of the reference display;   protected colors that should not be altered during pre-display processing by the video processor or during display configuration;   an image histogram characterizing the image in terms of luminance or gamut (for example, such information may be used by downstream devices to determine average luminance to refine tone and gamut mapping);   a scene change or reset flag, to alert downstream devices that any statistics or hysteresis from previous video frames are no longer valid;   a motion map characterizing the video content to identify objects in motion, which may be used by downstream devices in combination with the light source location map to guide tone and gamut mapping;   an indication of the source of color-timed content (e.g. direct from the camera, or post-production editing);   director=s creative intent settings which may be used to control downstream devices such as a decoder/television or other display. For example, such settings may include: display mode control providing the ability to control the display to operate in a particular mode (e.g. vivid, cinema, standard, professional, etc.); content type (e.g. animation, drama, sports, games, etc.) which may be used to determine an appropriate gamut or tone mapping or the like; tone mapping (e.g. customized tone mapping parameters or curves which may be used to guide tone expansion at the display); and gamut mapping (e.g. customized gamut mapping parameters which may be used to guide gamut expansion at the display);   and/or the like.       

     Video data  203  is delivered to a display subsystem at block  206 . As seen in  FIG. 3A , block  206  delivery may include an encoder stage  207 A for driving distribution, broadcast or transmission of video data  203  over a video distribution medium  205  such as satellite, cable, or high-definition networks; IP or wireless networks; or DVD or other storage media, etc. A decoder stage  207 B may be provided at the display end of block  206  to decode video data  203  distributed over medium  205 . Decoder stage  207 B may be implemented by a set-top box, for example, or by a decoder within the display subsystem. At blocks  206  and/or  208 , viewing environment metadata  225 C and/or other metadata  225  may be embedded in video data  203 . Viewing environment metadata  225 C may comprise, for example:
         Advanced Video Coding (AVC) VDR encoder data providing reference monitor tone mapping or gamut curves or ambient luminance of the reference environment. At least some of this information may be determined at the decoder stage  207 B (or by the video processor) with knowledge of the display characteristics (e.g. by reading the Extended Display Identification Data (EDID) of the display) and environment of the display subsystem. In some embodiments, at least some of this information may be determined at the studio during post-production processing of the video data.   Parameters describing the environment in which the display of the display subsystem is situated. Such parameters may include, for example, ambient luminance and/or tone or color temperature.
 
Viewing environment metadata  225 C may be used to guide processing of video data at block  208  and/or display configuration at block  210 .
       

     The display subsystem comprises a video processor for processing incoming video data  203  at block  208 . The video processor of the display subsystem may perform signal processing on video data  203  based on metadata  225  extracted from video data  203  (e.g. metadata  225 A) and/or known display characteristics associated with the display of the display subsystem. Video data  203  may be processed and adjusted for the display in accordance with display characterization parameters  226  and/or metadata  225 . 
     Other metadata  225  that may be embedded in video data  203  at blocks  206  and/or  208 , or at other stages of video delivery pipeline  200 , includes housekeeping metadata  225 D (for managing distribution rights and the like) such as, for example:
         watermarking data indicating where the video content was generated, distributed, modified, etc.;   fingerprinting data providing a description of the video content for searching or indexing purposes, and the like;   protection data indicating who owns the video content and/or who has access to it;   and/or the like.       

     Viewing environment metadata  225 C may be generated based at least in part on display characterization parameters  206  associated with the display of the display subsystem. In some embodiments, viewing environment metadata  225 C, source video content characterization metadata  225 B 2  and/or housekeeping metadata  225 D may be created or provided by analysis of video data  103  at the encoder stage  207 A, the decoder stage  207 B and/or by the video processor at block  208 . 
     At block  210 , display configuration may be performed on a display of the display subsystem. Appropriate parameters for display configuration may be determined based on display characterization parameters  226  and/or metadata  225 , such as camera metadata  225 A, post-production metadata  225 B (including reference display and environment metadata  225 B 1  and source video content characterization metadata  225 B 2 ) and viewing environment metadata  225 C. The display is configured in accordance with such parameters. Video data  203  is output to the display. 
     As metadata  225  is generated at blocks  202 ,  204 ,  206  or  208  for a video frame delivered through video delivery pipeline  200 , metadata  225  may be serially written in available guard bits and/or LSBs of video frames delivered through the pipeline. The required metadata bandwidth may vary between video frames, depending on the frequency and size of metadata transmission for particular metadata types. According to certain embodiments, some types of metadata  225  may be transmitted downstream every 10 seconds or so (e.g. this may include reference display and environment metadata  225 B 1 ); other types of metadata  225  may be transmitted downstream once per frame sequence or once per scene change (e.g. this may include viewing environment metadata  225 C); and still other types of metadata  225  may be transmitted once per frame or once every few frames (e.g. this may include some parameters of source video content characterization metadata  225 B 2 ). 
     For some video frames, it may be possible to sequentially embed all of metadata  225  generated at blocks  202 ,  204 ,  206  or  208  within the guard bits or LSBs of one video frame. For other video frames, metadata  225  generated at blocks  202 ,  204 ,  206  or  208  may require more than one video frame to deliver, and may exceed the metadata bandwidth provided by video delivery pipeline  200 . This may result in non-delivery of metadata. As discussed in further detail below, systems, apparatus and/or methods are provided to manage the encoding and delivery of metadata  225  through video delivery pipeline  200  to ensure that metadata  225  is timely delivered and applied. 
     Metadata  225  that is used for processing of video data  203  at block  208  and display configuration at block  210  is delivered in the video data stream so that metadata  225  is received at the display subsystem (including the video processor and display) prior to its application. In some embodiments, metadata  225  is delivered so that it is received by the display subsystem at least one video frame ahead of the frame at which the metadata  225  is to be applied. In certain embodiments, metadata  225  is delivered one video frame ahead and application of metadata  225  at blocks  208  and/or  210  may be triggered upon detection of a new video frame in the incoming video stream. 
     In particular embodiments, systems and/or apparatus of video delivery pipeline  200  comply with a metadata protocol defining a metadata structure.  FIG. 6A  illustrates a metadata structure or packet  250  of metadata  225  according to a particular embodiment that may be generated, for example, at any one of blocks  202 ,  204 ,  206  or  208  of the video delivery pipeline  200  of  FIG. 3  and delivered downstream in the pipeline. Packet  250  is framed with a header. In the illustrated embodiment of  FIG. 6A , packet  250  includes the following fields:
         a start of frame (SOF) header  252  defining the header with a start of frame bit set;   a packet type  254  defining the type of metadata in the payload (e.g. gamut parameter, scene change flag, image histograms, etc.) and format or pattern of the subsequent metadata;   CFG bits  256  defining a configurable portion of the framing structure (e.g. CFG bits  256  may define whether a timestamp is enabled for the packet, and how to apply the timestamp);   metadata payload  258  which may be variable in length;   end of frame (EOF) header  260  defining the header with an end of frame bit set;   timestamp  262  (optional) indicating when data in metadata payload  258  is to be applied (e.g. a certain number of video frames or scenes after metadata packet  250  is received, or after some other delay); and   a checksum such as, for example, a CRC (cyclic redundancy check) value  264  to enable verification of metadata packet  250 .       

       FIG. 6B  illustrates a header  270  that may be used to define the start (i.e. SOF header  252 ) or end (i.e. EOF header  260 ) of a metadata packet  250  as shown in  FIG. 6A . In the illustrated embodiment, header  270  begins with a plurality of bits in a predetermined pattern  272 . Header  270  ends with an end of payload (EOP) flag or bit  266 , and an SOF/EOF flag or bit  268  (e.g. 0/1). The SOF/EOF flag  268  determines whether header  270  is an SOF header  252  or an EOF header  260 . The EOP flag  266  may be valid only if the EOF flag  268  is set. Setting the EOP flag  266  indicates that the metadata packet  250  contains the last portion of a metadata payload. The EOP flag  266  enables a metadata payload to be split among several metadata packets  250 , which may be split across video frames. The EOP flag  266  enables low priority metadata packets to be interrupted to transmit high priority metadata packets. 
     The EOP flag  266  enables packets carrying different types of metadata to be delivered over multiple video frames, as seen in  FIG. 10 . The type of metadata carried in a packet may be indicated by packet type  254  in the header (see  FIG. 6A ). In the illustrated example, a first packet  280  carrying type A metadata is embedded in video data of video frame  1 . During embedding of type A metadata in the video data stream, type B metadata, having a higher priority than metadata type A, is received. To interrupt transmission of type A metadata in favour of type B metadata, an EOF flag is set to conclude first packet  280  (however, the EOP flag is not set as there is remaining type A metadata to be transmitted). A second packet  282  carrying the type B metadata may then be embedded in video data of video frame 1. In the illustrated example, video frame 1 does not have sufficient guard bits or LSBs for delivery of all of the type B metadata. Thus, toward the end of video frame 1 an EOF flag is set to indicate the end of second packet  282  (however, the EOP flag is not set as there is remaining type B metadata to be transmitted). A third packet  284  carrying the remaining type B metadata may be embedded in video data of video frame 2. The third packet  284  may be terminated with an EOF flag and an EOP flag to indicate the end of the packet and end of the metadata payload for the type B metadata. Delivery of type A metadata may then resume. In the illustrated example, all remaining type A metadata (which has been saved during embedding of metadata type B) is retrieved and carried in a fourth packet  286  of metadata embedded in the video data of video frame 2. The fourth packet  286  may be terminated with an EOF flag and an EOP flag to indicate the end of the packet and end of the metadata payload for the type A metadata. 
     According to particular embodiments, metadata bits are serialized onto bits (e.g. guard bits and/or LSBs) of video data in such a way so as to avoid inadvertently communicating a reserved or protected word or sequence of bits (which may be any number of bits long). There may be two types of reserved words: reserved metadata words as may be communicated by the metadata, and reserved video words as may be communicated by the video data stream. The metadata may be encoded so that the metadata payload avoids matching a reserved metadata word, such as a packet end of frame or EOF header  260  ( FIG. 6A ). In embodiments where guard bits of video data are overwritten with metadata, the serialized metadata should avoid overriding the function of the guard bits, which is to prevent reserved video words from being communicated by the video data. For example, in some video formats such as VDR or HDMI formats, the guard bits are used to ensure that certain reserved video words (e.g. reserved pixel values) are not transmitted. Reserved pixel values may include, for example, 0, 255 and other reserved values. 
       FIG. 4A  illustrates a method  300  of encoding metadata bits in video data so as to avoid communication of reserved video words. Method  300  may be applied to serialization of metadata in video data in a VDR or other video format which uses guard bits. Method  300  begins at block  302  by receiving metadata to be carried in the video data stream. The metadata may be received, for example, from a metadata generator or encoder at any one of blocks  202 ,  204 ,  206  or  208  of video delivery pipeline  200  shown in  FIG. 3 . In certain embodiments, the metadata received at block  302  is metadata to be applied at future video frames (e.g. for processing of video data and/or display configuration), so that the metadata is delivered in the video data stream at least one video frame ahead of the frame at which the metadata is to be applied. The metadata may be encoded as a metadata packet (e.g. a metadata packet  250  as shown in  FIG. 6A ). At block  304 , the first bit in the metadata packet is retrieved and the next available guard bit is located in the video data stream (i.e. a guard bit which has not been overwritten with metadata). At block  306 , the video data stream (in some embodiments including previously transmitted metadata) is considered to determine whether the guard bit may be required as a guard to prevent unintentional communication of one or more reserved video words. If conditions are such that the guard bit should be used as a guard, a guard is inserted in the guard bit at block  310 . In other embodiments, guards may be written in the guard bits during encoding of video data; therefore a guard may already be contained in the guard bit and the guard bit may be skipped at block  310 ; no metadata bit is inserted in the skipped guard bit. 
     The block  306  guard conditions for inserting a guard may include, for example, considering whether bits in the video data stream preceding the guard bit are close to matching (e.g. are one bit short of matching) a reserved video word. This determination may be made by comparing the preceding bits in the video data stream to each word in a list of reserved video words. 
     After inserting a guard in the guard bit at block  310  (or skipping the guard bit), the next guard bit is located in the video data stream at block  312  and the block  306  test is applied to this next guard bit to determine whether the guard bit should be used as a guard (or whether metadata may be written in the guard bit). 
     If it is determined at block  306  that a particular guard bit is not required to be used as a guard, then the bit of metadata may be written in the guard bit at block  308 . As long as there are remaining bits of the metadata packet to be embedded in the video data stream (see block  314 ), subsequent bits are retrieved from the metadata packet and subsequent guard bits are located in the video data stream (see block  316 ). For each metadata bit retrieved and guard bit located, the block  306  test is applied to determine whether to treat the guard bit as a guard (block  310 ) and skip to the next guard bit (block  312 ); otherwise, metadata may be written in the guard bit (block  308 ). 
     In particular embodiments, the block  306  guard conditions are evaluated by considering the bits of pixel data  305  immediately prior to the guard bit to determine if a reserved video word could potentially be communicated by the video data. For example, for video formats where reserved video words comprise certain pixel values such as 0 and 255 (e.g. represented in binary form as 00000000 and 11111111, respectively), the seven bits of pixel data  305  preceding the guard bit may be considered at block  306 . If the preceding seven bits are all consecutive zeros or consecutive ones, then the guard bit (which would be the eighth bit in the series of video data bits) should function as a guard. The guard bit may be set with an appropriately selected guard of 0 or 1 at block  310  to prevent communication of a reserved video word. Reserved video words may comprise other words or sequences of bits of various lengths. The block  306  guard conditions may evaluate pixel data  305  to detect potential communication of any of these reserved video words. 
     Metadata  225  may be encoded so as to avoid unintended communication of reserved metadata words. Reserved metadata words may include, for example, a packet start of frame header defining the start of a metadata packet or a packet end of frame header defining the end of a metadata packet. Encoding methods used to avoid unintended communication of reserved metadata words may include, for example:
         6b/8b encoding (wherein the longest permitted run of consecutive identical bits is 6 bits long).   8b/10b encoding (wherein the longest permitted run of consecutive identical bits is 5 bits long).   Defining a fixed pattern of consecutive identical bits to represent reserved metadata words such as SOF header  252  or EOF header  260 , and avoiding encoding the fixed patterns during embedding of the metadata payload in the video data. For example, if the fixed patterns are the six bit long patterns 000000 and 111111, whenever the five bit long pattern 00000 or 11111 appears in the metadata payload, a 1 or 0 guard bit is embedded as the next bit in the video data stream (e.g. 000001 or 111110). During extraction of metadata from the video data stream, this guard bit is not considered valid and is disregarded.       

       FIG. 4B  shows a method  330  of retrieving metadata bits that have been encoded using method  300  of  FIG. 4A  from a video signal. Method  330  begins by receiving a stream of video data  332  and monitoring video data  332  at block  333  to detect an SOF header  252  (see  FIG. 6B ) or other reserved metadata word defining the start of a metadata packet. Detection of the start of a metadata packet at block  333  may include receiving and decoding guard bits in video data stream (and skipping guard bits that are used as guards to prevent communication of reserved video words) until a series of metadata bits forming an SOF header  252  is detected. After the start of a metadata packet has been detected at block  333 , method  300  proceeds by locating the next guard bit in the video data stream at block  334 . At block  336 , preceding video data  335  (i.e. video data bits received immediately prior to the guard bit) is considered to determine whether the guard bit is functioning as a guard so as to prevent communication of a reserved video word in the video data stream. If it is determined at block  336  that the guard bit is not being used as a guard (i.e. metadata is written in the guard bit), metadata is extracted from the guard bit at block  338 . 
     If it is determined at block  336  that the guard bit is being used as a guard, the next guard bit in the stream of video data  332  is located at block  334 , and the block  336  test is applied to this next guard bit to determine whether the guard bit is being used as a guard (otherwise, the guard bit contains metadata that may be extracted at block  338 ). 
     In particular embodiments, the block  336  evaluation may be performed by comparing bits of video data  335  immediately prior to the guard bit with fixed patterns of bits indicative of reserved video words. Block  336  determines whether a reserved video word could potentially have been communicated by the video data if a guard were not inserted in the guard bit. If a reserved video word could potentially have been communicated, then it may be assumed that the guard bit is being used as a guard and method  300  proceeds to block  334  by locating the next guard bit in the video data stream. However, if a reserved video word could not have been communicated, then it may be assumed that the guard bit contains metadata, which may be extracted from the guard bit at block  338 . 
     In other embodiments, metadata is written in the LSBs  12  of the chrominance channels of a video frame (e.g. see  FIG. 2B ) instead of in the guard bits  11  of a video frame (e.g. see  FIG. 2A ). Metadata  225  may be encoded in the LSBs  12  so as to avoid unintended communication of reserved metadata words (e.g. a start of frame header or end of frame header). Metadata  225  may be encoded using one of the methods described above (e.g. 6b/8b encoding, 8b/10b encoding, defining the reserved words as fixed patterns of consecutive identical bits, etc.) to avoid unintended communication of reserved metadata words. The image quality in video content display may be affected as a result of overwriting bits of chrominance data such as LSBs  12 . Particular methods of encoding metadata in LSBs may be used to reduce adverse impact on image quality.  FIG. 5A  shows a method  400  that may be used for encoding metadata in LSBs  12  of chrominance channels of a video frame (e.g. see  FIG. 2B ). Method  400  evaluates different ways of encoding metadata in LSBs  12  of chrominance channels. The selected manner of encoding metadata may affect the image quality in video content display. 
     Method  400  begins at block  402  by receiving metadata  225  for the next (future) M video frames. The metadata  225  received at block  402  is metadata to be applied at future video frames (e.g. for video processing and/or display configuration), so that it may be delivered in the video data stream at least one video frame ahead of the frame at which the metadata is to be applied. Method  400  proceeds by considering whether metadata  225  may be embedded in a certain way to minimize artifacts during display. For example, metadata  225  may be written in LSBs of chrominance channels of pixels representing brighter areas of an image (e.g. pixels in which luminance exceeds some threshold), given that changes in a displayed image caused by overwriting the LSB tend to be less noticeable in brighter image areas. In some embodiments, metadata is written to LSBs of chrominance data for pixels in which chrominance values exceed some threshold. At block  406  of method  400 , bright image areas to be displayed by the video frames are identified. An assessment is made at block  408  as to whether the pixels representing the bright image areas provide sufficient bandwidth to transmit metadata  225 . If there is sufficient bandwidth, metadata  225  may be written in the LSBs of chrominance channels of pixels in the brighter image areas at block  410 . Otherwise, method  400  may proceed by evaluating another method of writing metadata  225 . Prior to writing metadata  225  in the pixels of brighter image areas at block  410 , a first metadata packet may be transmitted in the video data stream in the default manner (e.g. writing in the LSB of each chrominance channel) to indicate to the video receiver or processor the area(s) in the video frame in which subsequent metadata  225  is encoded. 
     Method  400  may evaluate at block  412  whether writing of metadata  225  in round robin fashion (or in some other manner which skips LSBs so as to minimize artifacts in the displayed image) would provide sufficient bandwidth for transmission of metadata  225 . If sufficient bandwidth would be available, at block  414  metadata  225  is written in the LSBs of chrominance channels of video frames in round robin fashion (e.g. a first pixel has an embedded metadata bit in the red channel only, a second pixel has an embedded metadata bit in the green channel only, a third pixel has an embedded metadata bit in the blue channel only, etc.). Prior to writing metadata  225  in round robin fashion, a first metadata packet may be transmitted in the video data stream in the default manner (e.g. writing in the LSB of each chrominance channel) to signify to the video receiver or processor that the metadata  225  that follows is written in round robin fashion. The first metadata packet may indicate where in the video frame the metadata  225  (written in round robin fashion) is embedded. The first metadata packet may provide for methods of synchronizing of metadata delivery between the transmitting and receiving ends of the video delivery pipeline. 
     If insufficient bandwidth is provided by a round robin manner of writing metadata, at block  416  a default method of embedding metadata may be applied (e.g. metadata  225  may be written in each LSB of chrominance channels in the video frames). If any metadata  225  remains which has not yet been embedded in the video data stream after writing of metadata  225  at block  416  (see block  422 ), delivery of the remaining metadata  225  may be prioritized and managed at block  424 . Metadata  225  may be split into multiple packets for transmission. Using an EOP flag, transmission of metadata packets may be interrupted in favour of transmission of metadata packets of a higher priority, as described herein with reference to  FIGS. 8 and 10 . 
       FIG. 5B  shows a method  425  that may be used for encoding metadata by overwriting chrominance data in a video frame to provide bursts of metadata. For example, chrominance portions for pixels in black frames or black image areas (where luminance values for the pixels are at zero or are below some threshold) may be used for carrying metadata, as the chrominance data for such pixels may be overwritten without substantially affecting image quality. A large number of pixels have luminance values of zero or a very small value in the following kinds of frames, for example:
         Black frames, such as may be used to transition between different scenes of a film, or between commercials and scheduled programming, for instance.   Frames of particular video formats, such as letterboxed, pillarboxed and windowboxed formats in which the video image is displayed with mattes or black bars at the sides and/or above and below the video image. Such formats are typically used to preserve the video=s original aspect ratio on a display.       

     Method  425  begins at block  426  by receiving metadata  225  for the next M video frames. At block  428 , method  425  identifies any black frames (or black image areas) in the current video frames which may be used to carry metadata bursts. At block  430 , a plurality of bits of metadata  225  are written within the chrominance channels of pixels in the identified black frames (or black image areas). For example, a series of metadata bits  13  may be inserted in chrominance channels as shown in  FIG. 2C  so as to overwrite the chrominance data. Prior to writing metadata  225  in the chrominance channels, a first metadata packet may be transmitted in the video data stream in the default manner (e.g. writing in LSBs) to provide information which signals to the video data receiver or processor that the metadata  225  that follows is written in the chrominance channels for the pixels. 
     At block  432 , if any metadata  225  remains (i.e. which is not written in the chrominance channels of pixels in the black frames), such metadata  225  may be written in the available LSBs in the current non-black video frames. If after all available LSBs have been filled, there remains metadata  225  that has not yet been embedded in the video data stream (see block  434 ), delivery of the remaining metadata  225  may be prioritized and managed (block  436 ). Particular methods for prioritizing metadata are described in further detail below with respect to  FIG. 8 . 
     For certain video formats, video images may be displayed with mattes or black bars at the sides and/or above and below the video image. When video data is provided in such formats, metadata  225  may be embedded within the chrominance channels of the pixels representing the black mattes or bars. 
     In other embodiments, a method which is a variation of or a combination of steps of methods  300 ,  400  and/or  425  may be applied to manage metadata delivery. For example, a particular method may combine the steps of providing metadata bursts by overwriting chrominance data in black video frames and/or areas, and writing metadata in guard bits or in LSBs of chrominance channels in non-black video frames. 
     Each method that is applied to encode metadata  225  in the video data stream may incorporate steps to ensure that a reserved video word is not unintentionally communicated by the video data. For example, methods similar to those described above with reference to  FIGS. 4A and 4B  may be performed in which the preceding video data transmitted is considered and compared to lists of reserved video words, and if appropriate, a guard is set in the guard bit to protect against communication of the reserved video words. 
       FIG. 8  is a flowchart illustrating a method  500  for managing delivery of metadata according to one embodiment. According to method  500 , transmittal of metadata through the video delivery pipeline may be temporarily interrupted to allow transmittal of other metadata categorized as relatively higher priority metadata. Interruption of metadata delivery may be required given that there are multiple stages along video delivery pipeline  200  at which metadata may be generated and embedded in the video data stream. For certain video frames (e.g. video frames which have metadata generated at multiple stages of the video delivery pipeline), there may be insufficient metadata bandwidth available to deliver metadata  225  to a downstream device prior to the time at which metadata  225  is to be applied by the downstream device. 
     Method  500  may be performed if there is new metadata that is to be embedded in a video data stream, but the current video frames in the video data stream do not have the metadata bandwidth for carrying the new metadata and existing metadata. For example, existing metadata  225  may have already been embedded in the current video frames at a previous stage of the video delivery pipeline, leaving insufficient bandwidth for delivery of new metadata.  FIG. 8  begins at block  502  by locating and retrieving an existing metadata structure which is embedded in the video data stream. The priority of the existing metadata structure and the priority of the new metadata structure to be transmitted are determined at block  504 . In certain embodiments, particular metadata types may be assigned a particular priority level. Therefore, the priority determination at block  504  may be based on metadata type as defined in the frame header. At block  508 , the priorities determined at block  504  are compared. If the priority of the new metadata structure to be transmitted is lower than the priority of the existing metadata structure embedded in the video data stream, method  500  proceeds to block  502  by retrieving the next metadata structure which is embedded in the video data stream. The steps at blocks  502  to  508  may be repeated until an existing metadata structure is located in the video data stream which has a lower priority than the new metadata structure to be transmitted (or until metadata bandwidth in the video data stream becomes available). 
     If at block  508 , the priority of the new metadata structure to be transmitted is higher than the priority of the existing metadata structure embedded in the video data stream, method  500  interrupts transmission of the existing metadata structure at block  510  by extracting existing metadata  515  from the video data stream and storing the existing metadata  515  for later transmittal. At block  512 , the video data guard bits or LSBs previously occupied by metadata  515  are overwritten with the new metadata structure to be transmitted. 
     If after overwriting the video data guard bits or LSBs previously occupied by metadata  515  with new metadata (see block  512 ), there is remaining new metadata that needs to be transmitted (see block  514 ) and limited metadata bandwidth is available for such transmission, method  500  may proceed by retrieving the next existing metadata structure embedded in the video data stream (block  502 ) and comparing its priority to that of the new metadata (block  504 ). If the priority of the remaining new metadata to be transmitted is higher, transmission of the existing metadata structure may be interrupted as described above in favor of transmission of the new metadata at blocks  510  and  512 . 
     If there is no further new metadata to be transmitted (block  514 ), transmission of existing metadata  515  may resume. This may be accomplished by rewriting metadata  515  to guard bits or LSBs in the video data stream at block  516 . 
     In some situations, metadata is embedded in and delivered contemporaneously within the video frames for which the metadata is to be applied during processing or display of the video frames. In other situations, metadata which is to be applied for a particular video frame may be transmitted with the video data for one or more earlier video frames. Metadata may be delivered to and received by a video decoder, processor or other downstream device in advance of the particular video frame at which the metadata is to be applied. To facilitate processing of and application of metadata, the metadata packet(s) carrying a metadata payload may include a timestamp indicating when the metadata is to be applied. In some embodiments, the timestamp may be defined in terms of a frame delay indicating that the metadata is to be applied at a certain number of video frames after the metadata has been received. In other embodiments, the timestamp may be defined in terms of a time delay, a frame sequence number, a time relative to the start of the video, or the like. 
     In some embodiments, metadata may be carried in the pixel data for a black frame inserted between scene transitions or within a scene. At the display end (block  210  of  FIG. 3 ), the display may repeat playback of the video frame preceding the black frame, to avoid interruption in the display of the scene while metadata in the black frame is being extracted and/or applied. Prior to writing metadata in the pixel data for the black frame, a first metadata packet may be transmitted in the video data stream in the default manner (e.g. writing in the guard bit or writing in the LSB of each chrominance channel) to signify to the downstream device that the metadata  225  that follows is written in a black frame. In certain embodiments, the display may playback the black frame containing metadata. In other embodiments, the display may not playback the black frame containing metadata (i.e. display of the black frame is skipped). The display may repeat playback of the video frame preceding the black frame, while extracting and/or applying metadata from the black frame. 
       FIG. 7  shows metadata  225  that is carried through a video delivery pipeline and received by a downstream device (e.g. video processor, decoder and/or display) in advance of the time at which the metadata is processed and applied. Metadata  225  includes six metadata payloads, each associated with a video frame (i.e. one of video frames #3 through #9). As seen in  FIG. 7 , while the metadata payload associated with video frame #3 is being delivered to a downstream device, the downstream device is processing video frames #1 and 2. A timestamp for the metadata payload associated with video frame #3 may indicate that the metadata payload is to be applied three frames after the metadata payload is received. 
     The use of timestamps may facilitate delivery of all metadata for a scene to ensure that such metadata is available to a downstream device prior to application of the metadata by the downstream device (e.g. metadata may be applied for processing of video data and/or display configuration for the scene). The metadata may be embedded in video data during a scene transition (e.g. the metadata may be delivered with black frames inserted between scenes). The metadata may be embedded in chrominance data in frames or areas of a frame where luminance values are driven to zero (e.g. using the methods described herein with reference to  FIG. 5B ). In embodiments where uncompressed video data is delivered at block  206  (FIG.  3 ), timestamps may be used to manage delivery of metadata in the video data between the encoder at encoder stage  207 A and the video processor/decoder at block  208  ( FIG. 3A ). 
       FIG. 9  shows a system  600  according to one embodiment that may be configured to perform one or more of the methods described herein. Components of system  600  may be implemented as software, hardware and/or a combination thereof. System  600  includes a video capture subsystem  602 , a post-production subsystem  603  and a display subsystem  604 . A stream of video data  203  is generated by video capture subsystem  602  and is delivered to post-production subsystem  603  for processing and editing. Video images may be displayed and viewed on a reference display  111  of post-production subsystem  603  in the course of editing the video data  203 . The edited video data  203  is delivered to display subsystem  604  (over a distribution medium  205  by way of encoder  207 A and decoder  207 B) for further processing and display. Each of subsystems  602 ,  603  and  604  (and encoder  207 A) may be configured to encode metadata  225  in video data  203 . Downstream subsystems may be configured to receive video data  203  from an upstream device and decode the metadata  225  which has been embedded therein. Metadata  225  may be used by downstream subsystems (e.g. subsystems  603  and  604 ) to guide processing and/or display of video data  203 . Metadata  225  may be used by display subsystem  604  along with display characterization parameters  620  to control and/or guide video playback on a display  618  of display subsystem  604 . 
     As seen in  FIG. 9 , subsystems  602 ,  603  and  604  may comprise a processor  606 ,  608  and  616  respectively, and a program memory  607 ,  609  and  617  accessible to the respective processors. Each processor may comprise a central processing unit (CPUs), one or more microprocessors, one or more field programmable gate arrays (FPGAs), or any combination thereof, or any other suitable processing unit(s) comprising hardware and/or software capable of functioning as described herein. In each subsystem the processor executes instructions provided by software stored in the program memory. The software may include routines to perform the metadata generation, encoding, decoding and processing steps described herein, such as, for example, routines which:
         generate metadata  225  or receive parameters for metadata  225  (e.g. such parameters may be set by color timers or color graders at the post-production stage; metadata  225  may define certain parameters as described herein with reference to  FIG. 3 );   decode metadata  225  from video data  203  received from an upstream device;   process and apply metadata  225  to guide processing and/or display of video data;   encode metadata  225  in video data  203  before such video data is communicated to a downstream device;   interrupt delivery of lower priority metadata  225  so as to allow for delivery of higher priority metadata  225  in the video data stream;   select a method for encoding metadata  225 , based on the image and/or video data  203  (e.g. the method of encoding metadata  225  may be selected to minimize adverse effects on image quality);   manage encoding of bursts of metadata  225  in chrominance portions of video frames, areas of video frames or pixels for which luminance values are zero or below a threshold value;   and/or the like.       

     System  600  may include a repository  610  accessible to subsystems  602 ,  603  and  604 . Repository  610  may include a library of metadata definitions  612  (e.g. which informs the metadata encoders and decoders as to how to generate and/or read the metadata) and a list of reserved video words  614  (e.g. protected pixel values). The library of metadata definitions  612  may be accessed by subsystems  602 ,  603  and  604  in generating, encoding and/or processing metadata. In encoding or decoding metadata  225 , reserved video words  614  may be compared to video data bits preceding a guard bit as described above to identify whether the guard bit is treated as a guard to prevent communication of reserved video words. 
     While a shared repository  610  is shown in the illustrated embodiment of  FIG. 9 , in other embodiments each of subsystems  602 ,  603  and  604  may incorporate a local repository  610  stored in a storage medium accessible to that subsystem. 
       FIG. 11A  shows a subsystem  280  that may be used to encode metadata in a stream of video data according to an example embodiment. Subsystem  280  may be used to encode metadata  225  relating to an upcoming scene or other sequence of frames, using method  300  shown in  FIG. 4A , for example, or another method described herein. Subsystem  280  may receive input video data  203  from a source of video data. In some embodiments, subsystem  280  may retrieve input video data  203  from a buffer or other storage media. In other embodiments, subsystem  280  may receive streaming video data  203  from a video signal input. Video data  203  may be provided in a format suitable for the type of video content delivery, such as television broadcast over satellite, cable, or high-definition networks; streaming multimedia over IP or wireless networks; or reading a DVD or other storage media, or the like. 
     Input video data  203  may include embedded metadata which was added to the video data by an upstream apparatus. According to some embodiments, input video data  203  may include guard bits. Input video data  203  may contain luminance and chrominance information. In particular embodiments, video data  203  is decoded by a decoder  282 . Decoder  282  may separate the luminance and chrominance components in the video signal. 
     Video data  203  for the upcoming scene or sequence of frames may be pushed into one or more data buffers  283  implemented by software and/or hardware. One or more frames of video data  203  (or other portion of video data  203 ) may be pushed into buffer  283 , in succession, as video data  203  is received. In some embodiments, guard bit reader  284  determines where to begin inserting metadata in the video data stream, by monitoring the guard bits of the buffered video data  203  in buffer  283  (skipping those bits that contain a guard) until a reserved metadata word (e.g. end of metadata payload, or the like) is detected; new metadata  225  may be written in the video data after such reserved metadata word. In other embodiments, guard bit reader  284  may receive a signal or read a metadata packet indicating the location in the video data stream  203  at which subsystem  280  may commence encoding metadata in the video stream. 
     To begin encoding metadata, guard bit reader  284  accesses the video data  203  stored in buffer  283  and considers each guard bit in turn. For each guard bit considered, guard bit reader  284  may compare video bits preceding the guard bit to each of a plurality of reserved video words (e.g. reserved pixel values) accessed from a reserved word store  285 . Based on such comparison, guard bit reader  284  may identify whether the guard bit is functioning as a guard to prevent communication of reserved video words, or whether the guard bit may contain metadata. 
     If guard bit reader  284  determines that the guard bit may contain metadata, guard bit reader  284  may send a signal  287  to data writer  286  communicating that metadata  225  (or other data) may be written in the guard bit (as discussed in respect of block  308  of  FIG. 4A , for example). Guard bit reader  284  may continue to access and read video data  203  in buffer  283  until all of the metadata  225  for a particular scene or sequence of frames has been written in video data  203 . 
     When data writer  286  receives signal  287 , data writer  286  retrieves the next bit of metadata  225  relating to the upcoming scene. Data writer  286  writes this bit of metadata  225  in the guard bit determined by guard bit reader  284  to be suitable for carrying metadata. Data writer  286  may retrieve metadata  225  from a store or buffer containing metadata. After data writer  286  has written metadata  225  in all of the available guard bits of video data  203  in buffer  283 , subsystem  280  outputs video data  203  including the inserted metadata  225  (e.g. video data  203  may be pushed out from buffer  283  and new incoming frames of video data  203  are pushed into buffer  283 ; metadata  225  may then be written in the new frames of video data  203  in buffer  283 ). Output video data  203  may be delivered to a downstream apparatus such as a display subsystem for processing and/or video playback. 
     If guard bit reader  284  identifies that a guard bit is not suitable for carrying metadata (as it contains a guard), guard bit reader  284  may communicate a signal  288  to data writer  286  causing data writer  286  to insert a guard in the guard bit (as discussed with reference to block  310  of  FIG. 4A , for example). In other embodiments, signal  288  or lack of assertion of signal  287  may cause data writer  286  to skip the guard bit. As such, data writer  286  does not write any metadata  225  in this guard bit. 
       FIG. 11B  shows a subsystem  290  that may be used to decode metadata from a stream of video data according to an example embodiment. Subsystem  290  may be used to extract metadata  225  for an upcoming scene, using one of the methods described herein, such as, for example, method  330  of  FIG. 4B . Subsystem  290  is similar in some respects to subsystem  280 . For example, subsystem  290  receives input video data  203 , and may decode input video data  203  at a decoder  292  (similarly to how subsystem  280  receives and decodes input video data  203 ). Input video data  203  may be buffered in a buffer  293 . A guard bit reader  294  accesses the video data  203  stored in buffer  293  and considers each guard bit in turn. For each guard bit considered, guard bit reader  294  may compare video bits preceding the guard bit to each of a plurality of reserved video words (e.g. reserved pixel values) accessed from a reserved word store  295 . Based on such comparison, guard bit reader  294  may identify whether the guard bit is functioning as a guard to prevent communication of reserved video words, or whether the guard bit may contain metadata. 
     If it is determined by guard bit reader  294  that a guard bit may contain metadata, guard bit reader  294  may send a signal  297  to a metadata reader  296  causing metadata reader  296  to read the guard bit (as performed at block  338  of  FIG. 4B , for example). Metadata  225  that is read from the guard bits may be stored in a metadata store  296  for subsequent retrieval and application. 
     If it is determined by guard bit reader  294  that a guard bit contains a guard, guard bit reader  294  may, in some embodiments, send a signal  298  to metadata reader  296  causing metadata reader  296  to skip reading the guard bit. In other embodiments, metadata reader  296  reads metadata from a guard bit only if it receives a signal  297 , and a lack of assertion of signal  297  causes the guard bit to be skipped by metadata reader  296 . 
     In some embodiments, guard bit readers  284 ,  294  may not need to monitor guard bits in the incoming video stream to locate where to begin encoding or decoding video data. When metadata is written in video data, a metadata packet may be generated by the metadata writer and inserted in the video data stream, indicating to downstream apparatus where to locate existing metadata in the video data (e.g. in certain video frames, or commencing at a particular pixel in a video frame, or in particular image areas, etc.). This metadata packet may be used by subsystem  280  to guide writing of additional metadata in the video data and may be used by subsystem  290  to guide extraction of metadata from the video data. This metadata packet may be useful for synchronizing delivery of metadata through the video delivery pipeline. The metadata packet may also indicate to the downstream apparatus the pixel value that should be used to drive the display, for the pixels where metadata is extracted. This enables metadata to be encoded in areas of an image having a constant hue. 
     In other embodiments, subsystem  280  and subsystem  290  may be adapted or reconfigured to write metadata in video data according to some other method. For example, for embodiments where LSBs of chrominance portions of video data are used to transport video data, a least significant bit writer may be provided in place of guard bit reader  284  and data writer  286  of subsystem  280 . Similarly, a least significant bit reader may be provided in place of guard bit reader  294  and metadata reader  296  of subsystem  290 . The least significant bit writer may access the video data  203  in buffer  283  and write metadata in the LSBs of chrominance portions of the video data. The least significant bit reader may access the video data  203  in buffer  293  and read metadata from the LSBs of chrominance portions of the video data. The least significant bit writer may encode the metadata in such a way so as to avoid unintentional communication of reserved metadata words (by using, for example, 6b/8b or 8b/10b encoding or the like, or defining the reserved words as fixed patterns of consecutive identical bits, etc). 
     Guard bit readers  284 ,  294  (and least significant bit readers or writers) may be implemented by a data processor, CPU, microprocessor, FPGA, or any combination thereof, or any other suitable processing unit capable of reading video data to determine luminance levels and comparing such luminance levels to a threshold value. Data writer  286  and metadata reader  296  may be implemented by a data processor, CPU, microprocessor, FPGA, or any combination thereof, or any other suitable processing unit capable of accessing video data  203  from a video data source and writing or reading bits of video data  203 . 
     Where a component (e.g. processor, decoder, encoder, device, display, etc.) is referred to above, unless otherwise indicated, reference to that component (including a reference to a Ameans@ should be interpreted as including as equivalents of that component any component which performs the function of the described component (i.e., that is functionally equivalent), including components which are not structurally equivalent to the disclosed structure which perform the function in the illustrated exemplary embodiments of the invention. 
     Particular embodiments may be provided in the form of a program product. The program product may comprise any medium which carries a set of computer-readable signals comprising instructions which, when executed by a data processor, cause the data processor to execute a method of the invention. Program products according to the invention may be in any of a wide variety of forms. The program product may comprise, for example, physical media such as magnetic data storage media including floppy diskettes, hard disk drives, optical data storage media including CD ROMs, DVDs, electronic data storage media including ROMs, flash RAM, or the like. The computer-readable signals on the program product may optionally be compressed or encrypted. 
     While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize certain modifications, permutations, additions and sub-combinations thereof. For example:
         In certain embodiments, metadata may be carried in a video data stream by embedding the metadata in bits which are not guard bits or LSBs. For example, metadata may be embedded in most significant bits (MSBs), in some embodiments. This may be performed by shifting the existing video data to the right by one bit and placing the metadata in the MSB.   The example embodiments described herein provide for systems, apparatus and methods useful in a video delivery pipeline. Such systems, apparatus and methods may be useful for delivery of other types of data.   In example embodiments, metadata is written in video data and transmitted with the video data through the video delivery pipeline. In other embodiments, other kinds of data may be written in video data and transmitted with the video data through the video delivery pipeline.   Metadata written in video data according to the embodiments described herein may be useful in guiding configuration, control and/or operation of other apparatus such as a video archiver, recorder, etc.
 
It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.
       

     Accordingly the invention may suitably comprise, consist of, or consist essentially of, any of element (the various parts or features of the invention and their equivalents as described herein, currently existing, and/or as subsequently developed. Further, the present invention illustratively disclosed herein may be practiced in the absence of any element, whether or not specifically disclosed herein. Obviously, numerous modifications and variations of the present invention are possible in light of the above teachings. It is therefore to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described herein. 
     Accordingly, the invention may be embodied in any of the forms described herein, including, but not limited to the following Enumerated Example Embodiments (EEEs) which described structure, features, and functionality of some portions of the present invention.
     EEE1 A method of providing video data to a display subsystem, comprising:
       (a) capturing a sequence of video frames to provide video data;   (b) editing on a reference display an image provided by the video data;   (c) generating metadata identifying configuration parameters of the reference display and characteristics of the edited image;   (d) embedding the metadata in the video data;   (e) delivering the video data including the embedded metadata to the display subsystem;   (f) extracting the metadata at the display subsystem; and   (g) configuring the display subsystem or processing the video data for the display subsystem based at least in part on the metadata.   
       EEE2 A method according to claim 1, wherein embedding the metadata in the video data comprises overwriting a plurality of guard bits in the video data.   EEE3 A method according to claim 2, wherein embedding the metadata in the video data comprises:
       (a) retrieving a bit of metadata from a metadata packet to be delivered;   (b) locating a first guard bit in the video data;   (c) comparing a plurality of video bits preceding the first guard bit to a first word indicative of a reserved video word; and   (d) writing the bit of metadata in the first guard bit if the plurality of video bits preceding the first guard bit differs from the first word.   
       EEE4 A method according to claim 3, wherein embedding the metadata in the video data comprises setting a guard in the first guard bit if the plurality of video bits preceding the first guard bit matches the first word.   EEE5 A method according to claim 4, wherein if the guard is set in the first guard bit, embedding metadata in the video data comprises:
       (a) locating a second guard bit in the video data which is subsequent to the first guard bit;   (b) comparing a plurality of video bits preceding the second guard bit to the first word; and   (c) writing the bit of metadata in the second guard bit if the plurality of video bits preceding the second guard bit differs from the first word.   
       EEE6 A method according to claim 5, wherein extracting the metadata comprises:
       (a) locating the first guard bit in the video data;   (b) determining whether the first guard bit contains a guard by comparing the plurality of video bits preceding the first guard bit to the first word; and   (c) extracting the first guard bit if it is determined that the first guard bit does not contain a guard.   
       EEE7 A method according to claim 6, wherein if it is determined that the first guard bit contains a guard, extracting the metadata comprises:
       (a) locating the second guard bit in the video data;   (b) determining whether the second guard bit contains a guard by comparing the plurality of video bits preceding the second guard bit to the first word; and   (c) extracting the second guard bit if it is determined that the second guard bit does not contain a guard.   
       EEE8 A method according to claim 1, wherein embedding the metadata in the video data comprises overwriting a plurality of least significant bits (LSB) of chrominance channels in the video data.   EEE9 A method according to claim 8, wherein embedding the metadata in the video data comprises:
       (a) retrieving a bit of metadata from a metadata packet to be delivered;   (b) locating a first LSB of a chrominance channel in the video data; and   (d) writing the bit of metadata in the first LSB.   
       EEE10 A method according to claim 1, wherein embedding the metadata in the video data comprises overwriting a plurality of chrominance bits in the video data for pixels having luminance values below a threshold value.   EEE11 A method according to claim 1, wherein embedding the metadata in the video data comprises:
       (a) identifying one or more black frames in the video data; and   (b) overwriting a plurality of chrominance bits for pixels in the one or more black frames with the metadata.   
       EEE12 A method according to claim 1, wherein embedding the metadata in the video data comprises:
       (a) identifying one or more black image areas in the video data; and   (b) overwriting a plurality of chrominance bits for pixels in the one or more black image areas with the metadata.   
       EEE13 A method according to claim 1, wherein embedding the metadata in the video data comprises:
       (a) inserting a black frame of video data between a pair of video data frames;   (b) embedding the metadata in the pixel data of the black frame.   
       EEE14 A method according to claim 13 comprising, while the metadata in the pixel data of the black frame is extracted at the display subsystem, repeating playback by the display subsystem of a video frame preceding the black frame of video data.   EEE15 A method according to claim 1, wherein delivering the video data including the embedded metadata to a display subsystem comprises:
       (a) receiving new metadata to be transmitted in the video data;   (b) identifying a priority level of the new metadata;   (c) identifying a priority level of the embedded metadata;   (d) comparing the priority level of the new metadata with the priority level of the embedded metadata; and   (e) if the priority level of the embedded metadata is lower than the priority level of the new metadata, interrupting delivery of the embedded metadata, and writing the new metadata in the video data.   
       EEE16. A method according to claim 15, wherein interrupting delivery of the embedded metadata comprises:
       (a) extracting the embedded metadata from the video data; and   (b) storing the extracted metadata.   
       EEE17 A method according to claim 16, comprising resuming transmission of the extracted metadata by rewriting the extracted metadata in the video stream after all of the new metadata has been written in the video data.   EEE18 A method according to claim 1, wherein delivering the video data comprises delivering the video data with the embedded metadata in advance of a video frame for which the embedded metadata is to be applied.   EEE19 A method according to claim 18, wherein the metadata includes a timestamp identifying when the embedded metadata is to be applied.   EEE20 A method according to any one of claims 1 to 19, wherein delivering the video data comprises delivery by one of the following transmission media: DVD, Blu-ray, satellite, cable or Internet.   EEE21 A method according to any one of claims 1 to 20, wherein the metadata is encoded in one of the following formats:
       (a) 6b/8b encoding; and   (b) 8b/10b encoding.   
       EEE22 A method according to any one of claims 1 to 21, wherein the metadata is encoded so that a start of frame header in the metadata is represented by a first fixed pattern of consecutive identical bits and an end of frame header in the metadata is represented by a second fixed pattern of consecutive identical bits.   EEE23 A system comprising:
       (a) a video capture subsystem for generating video data;   (b) a post-production subsystem having a reference display and a processor configured to receive and edit the video data generated by the video capture subsystem and display the video data on the reference display; and   (c) a display subsystem having a display and a video processor configured to receive the video data edited by the post-production subsystem and display the video data on the display;   wherein at least one of the video capture subsystem, post-production subsystem and display subsystem is configured to encode metadata in the video data for guiding subsequent processing or display of the video data.   
       EEE24 A system according to claim 23, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to encode metadata in the video data by embedding metadata in a plurality of guard bits of the video data.   EEE25 A system according to claim 23, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to encode metadata in the video data by embedding metadata in a plurality of least significant bits of the video data.   EEE26 A system according to claim 23, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to encode metadata in the video data by overwriting chrominance data in the video data with the metadata.   EEE27 A system according to claim 24, comprising one or more repositories, each repository storing a list of reserved video words, wherein each of the video capture subsystem, post-production subsystem and display subsystem is configured to locate a next available guard bit in the video data, retrieve the list of reserved video words from one of the repositories and compare the reserved video words to the video data to determine whether to insert a guard in the next available guard bit.   EEE28 A system according to any one of claims 23 to 27, wherein the processor of the post-production subsystem is configured to encode metadata in the video data identifying at least one of:
       configuration parameters of the reference display; and   luminance and gamut characteristics of an image provided by the video data.   
       EEE29 A system according to claim 28, wherein the video processor of the display subsystem is configured to decode metadata in the video data and apply the decoded metadata to configure the display of the display subsystem or process the video data to adjust for characteristics of the display of the display subsystem.   EEE30 A system according to claim 28, wherein the video processor of the display subsystem is configured to read the Extended Display Identification Data of the display of the display subsystem to process the video data to adjust for characteristics of the display of the display subsystem.   EEE31 A system according to any one of claims 23 to 30, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to:
       select a method of encoding metadata based at least in part on the video data; and   apply the selected method to encode metadata in the video data for guiding subsequent processing or display of the video data.   
       EEE32 A system according to any one of claims 23 to 31, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to manage delivery of metadata in the video data so as to allow delivery of relatively lower priority metadata to be interrupted in favour of delivery of relatively higher priority metadata.   EEE33 A system according to any one of claims 23 to 32, wherein the display subsystem is configured to receive video data by way of at least one of the following transmission media: DVD, Blu-ray, satellite, cable or Internet.   EEE34 A system according to any one of claims 23 to 33, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to encode metadata in one of the following formats:
       (a) 6b/8b encoding; and   (b) 8b/10b encoding.   
       EEE35 A system according to any one of claims 23 to 34, wherein the video capture subsystem, post-production subsystem and display subsystem are configured to encode metadata so that a start of frame header in the metadata is represented by a first fixed pattern of consecutive identical bits and an end of frame header in the metadata is represented by a second fixed pattern of consecutive identical bits.   EEE36 A method of encoding metadata in video data, the method comprising:
       (a) retrieving a bit of metadata to be carried in the video data;   (b) locating a first guard bit in the video data;   (c) comparing a plurality of video bits adjacent to the first guard bit to a first word indicative of a reserved video word; and,   (d) writing the bit of metadata in the first guard bit if the plurality of video bits differs from the first word.   
       EEE37 A method according to claim 36, wherein encoding the metadata in the video data comprises setting a guard in the first guard bit if the plurality of video bits adjacent to the first guard bit matches the first word.   EEE38 A method according to claim 37, wherein if the guard is set in the first guard bit, encoding metadata in the video data comprises:
       (a) locating a second guard bit in the video data which is subsequent to the first guard bit;   (b) comparing a plurality of video bits adjacent to the second guard bit to the first word; and   (e) writing the bit of metadata in the second guard bit if the plurality of video bits adjacent to the second guard bit differs from the first word.   
       EEE39 A method according to any one of claims 36 to 38, wherein encoding the metadata comprises encoding the metadata in one of the following formats:
       (a) 6b/8b encoding; and   (b) 8b/10b encoding.   
       EEE40 A method according to any one of claims 36 to 39, wherein the metadata is encoded so that a start of frame header in the metadata is represented by a first fixed pattern of consecutive identical bits and an end of frame header in the metadata is represented by a second fixed pattern of consecutive identical bits.   EEE41 A method of extracting metadata from video data, comprising:
       (a) locating a first guard bit in the video data;   (b) determining whether the first guard bit contains a guard by comparing a plurality of video bits adjacent to the first guard bit to one or more reserved video words; and   (c) extracting the first guard bit if it is determined that the first guard bit does not contain a guard.   
       EEE42 A method according to claim 41, wherein if it is determined that the first guard bit contains a guard, extracting the metadata comprises:
       (a) locating a second guard bit in the video data which is subsequent to the first guard bit;   (b) determining whether the second guard bit contains a guard by comparing a plurality of video bits adjacent to the second guard bit to the one or more reserved video words; and   (c) extracting the second guard bit if it is determined that the second guard bit does not contain a guard.   
       EEE43 A method comprising any new and inventive act, step, combination of acts and/or steps or sub-combination of acts and/or steps described herein.   EEE44 An apparatus comprising any new and inventive feature, combination of features or sub-combination of features described herein