Patent Publication Number: US-11641539-B2

Title: Headphone interaction with media playback system

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. non-provisional patent application Ser. No. 16/845,988, filed on Apr. 10, 2020, entitled “Headphone Interaction with Media Playback System,” which is incorporated herein by reference in its entirety. 
     U.S. non-provisional patent application Ser. No. 15/939,758 claims priority under 35 U.S.C. § 120 to, and is a continuation of, U.S. non-provisional patent application Ser. No. 15/939,758, filed on Mar. 29, 2018, entitled “Headphone Interaction with Media Playback System,” and issued as U.S. Pat. No. 10,623,844 on Apr. 14, 2020, which is incorporated herein by reference in its entirety. 
    
    
     FIELD OF THE DISCLOSURE 
     The disclosure is related to consumer goods and, more particularly, to methods, systems, products, features, services, and other elements directed to media playback or some aspect thereof. 
     BACKGROUND 
     Options for accessing and listening to digital audio in an out-loud setting were limited until in 2003, when SONOS, Inc. filed for one of its first patent applications, entitled “Method for Synchronizing Audio Playback between Multiple Networked Devices,” and began offering a media playback system for sale in 2005. The Sonos Wireless HiFi System enables people to experience music from many sources via one or more networked playback devices. Through a software control application installed on a smartphone, tablet, or computer, one can play what he or she wants in any room that has a networked playback device. Additionally, using the controller, for example, different songs can be streamed to each room with a playback device, rooms can be grouped together for synchronous playback, or the same song can be heard in all rooms synchronously. 
     Given the ever growing interest in digital media, there continues to be a need to develop consumer-accessible technologies to further enhance the listening experience. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Features, aspects, and advantages of the presently disclosed technology may be better understood with regard to the following description, appended claims, and accompanying drawings where: 
         FIG.  1    shows an example media playback system configuration in which certain embodiments may be practiced; 
         FIG.  2    shows a functional block diagram of an example playback device in accordance with aspects of the disclosure; 
         FIG.  3    shows a functional block diagram of an example control device in accordance with aspects of the disclosure; 
         FIGS.  4 A and  4 B  are example controller interfaces in accordance with aspects of the disclosure; 
         FIG.  5 A  shows an example system that illustrates example headphone interactions accordance with aspects of the disclosure; 
         FIG.  5 B  is an example message flow diagram in accordance with aspects of the disclosure; 
         FIG.  5 C  is another example message flow diagram in accordance with aspects of the disclosure; 
         FIGS.  6 A and  6 B  are an example user interfaces in accordance with aspects of the disclosure; 
         FIG.  7 A  shows an example system that illustrates example headphone interactions accordance with aspects of the disclosure; 
         FIG.  7 B  is an example message flow diagram in accordance with aspects of the disclosure; 
         FIG.  7 C  is another example message flow diagram in accordance with aspects of the disclosure; 
         FIG.  7 D  shows an example system that illustrates example headphone interactions accordance with aspects of the disclosure; and 
         FIG.  8    shows an example headphone interaction technique, according to example implementations. 
     
    
    
     The drawings are for the purpose of illustrating example embodiments, but it is understood that the inventions are not limited to the arrangements and instrumentality shown in the drawings. 
     DETAILED DESCRIPTION 
     I. Overview 
     Examples implementations described herein involve interactions between a media playback system that includes one or more playback devices that are designed to play audio content out loud and headphones, which are connectable to personal devices. Example personal devices, such as smartphones, tablets, and laptops, may execute various media playback applications that facilitate playing back music content via headphones connected to the personal device. Such personal devices may also execute a control application that facilitates remote control of the media playback system. Example implementations may facilitate transitioning between playback of out loud audio content on the one or more playback devices and headphone playback of the audio content. 
     For example, as noted above, a personal device may execute a control application to control playback devices of a media playback system. Such a personal device may be referred to as a “control device.” The control device, by way of the control application, may display a control interface that includes playback controls (e.g., transport controls such as play, pause, or skip track) to remotely control audio content playback by the media playback system, as well as search and browse controls to select audio content for playback on the media playback system. The control interface may also include contextual information about the media playback system, such as metadata of the audio content currently playing back and as the name(s) of playback devices within the media playback system that are playing back the audio content, among other examples. 
     While particular audio content (e.g., an audio track) is being played back on one or more playback devices of the media playback system, a control device may detect that headphones have been connected to the control device (e.g., via an analog headphone jack or a point-to-point personal area connection, such as Bluetooth®). In response to detecting the connection of headphones, the control device transitions playback from the one or more playback devices of the media playback system to playback on the control device via the headphones. In particular, the control device instructs the one or more playback devices to stop (or mute) playback of the particular audio content. The control device also retrieves the audio content from the audio source that was providing the particular audio content to the one or more playback devices and resumes playing the particular audio content via the one or more headphones. The audio source may be an audio streaming service, such as Pandora® and Spotify®. Alternatively, the audio source may be a television or other line-in connected devices (e.g. a vinyl player) from which the one or more playback devices are retrieving audio content. 
     The control device may also facilitate transitioning playback to the one or more playback devices. For instance, while playing back particular audio content via the headphones, a control device may detect that the headphones have been disconnected from the control device. In response to detecting the disconnection of the headphones, the control device transitions playback from the control device via the headphones to playback on the one or more playback devices of the media playback system. In particular, the control device stops playback of the particular audio content on the control device. The control device also instructs the one or more playback devices to resume playing the particular audio content, perhaps after receiving confirmation that playback should be resumed via a selectable control displayed on the control interface. 
     To illustrate, in one example, a first user and a second user may begin watching a TV show or movie on a television that is configured to output sound through a playback device of a media playback system. In examples herein, the playback device outputting sound for the television may be a soundbar-type playback device configured with HDMI, optical digital or other audio input from a television or the like. If the first user decides to go to sleep, the second user, to avoid disturbing the sleeping user, may plug in headphones to their smartphone (which is also a control device for the given playback device). When the smartphone detects connection of the headphones, the smartphone instructs the soundbar-type playback device to stop playing back the television audio (e.g., by muting the output). The control device resumes playback via the connected headphones by retrieving the television audio from the source, which in this example may be through the soundbar-type playback device, as this device is connected to the television or content source. As noted above, if the audio source is a network location remote from the playback device, the control device may retrieve the audio content directly from that source (e.g., from a server of a streaming audio service). 
     Continuing the above-example, the second user may intentionally or unintentionally disconnect the headphones from his smartphone, which may cause the smartphone to transition playback of the television audio back to the soundbar-type playback device. To avoid a disturbance from out loud playback on the soundbar-type playback device, the smartphone may display a selectable control prompting the second user to confirm that playback should resume on the soundbar-type playback device. The smartphone may additionally display a selectable control to optionally adjust a playback volume when playback resumes on the soundbar-type playback device. When the selectable control is selected, the smartphone stops playback via the headphones and instructs the soundbar-type playback device to play back the television audio. 
     In some implementations, the control device may automatically transition playback based on a policy. For instance, an example policy may cause the control device to automatically transition playback during daytime hours (e.g., 8 AM to 9 PM) and prompt for confirmation during nighttime hours (e.g., 9 PM to 8 AM). The control interface of the control application may include controls to set such policies for the media playback system. Different playback devices may have different policies (e.g., a playback device in the bedroom might be programed with different hours than a playback device in a basement den). 
     In some examples, a playback device may facilitate transition of audio playback. For instance, a playback device may receive, from a control device, an instruction to play back audio content. In response, the playback device retrieves and plays back the audio content. While playing back the audio content, the playback device may receive, from the control device, a message indicating that headphones are connected to the control device of the media playback system. In response, the playback device stops playback of the retrieved audio content and causes the control device to play back the audio content via the first headphones. 
     As noted above, example techniques may involve headphone interactions with a media playback system. Example implementations described herein may be embodied as a method, a device configured to carry out the implementation, a system of devices configured to carry out the implementation, or a non-transitory computer-readable medium containing instructions that are executable by one or more processors to carry out the implementation, among other examples. It will be understood by one of ordinary skill in the art that this disclosure includes numerous other embodiments, including combinations of the example features described herein. Further, any example operation described as being performed by a given device to illustrate a technique may be performed by any suitable devices, including the devices described herein. Yet further, any device may cause another device to perform any of the operations described herein. 
     A first implementation may include while headphones are disconnected from a first control device, receiving, via a network interface of the first control device, an indication of particular audio content being played back by a first zone of the media playback system, wherein the first zone comprises one or more playback devices that are separate and distinct from the first control device and connected to the first control device via a local area network; while the particular audio content is being played back by one or more playback devices of the media playback system, detecting that headphones have been connected to the first control device, wherein headphones are connectable to the first control device via either (a) an analog headphone jack of the first control device or (b) a point-to-point personal area network connection via a personal area network interface of the first control device; and in response to detecting that the headphones are connected to the first control device of the media playback system: (i) causing, via the network interface of the first control device, the one or more playback devices of the first zone to stop playback of the particular audio content; (ii) retrieving, via the network interface of the first control device, the particular audio content from an audio source that is remote from the first control device; and (iii) resuming playback of the particular audio content via the connected headphones. 
     A second implementation may include receiving, via a network interface from a first control device of the media playback system, an instruction to play back audio content; in response to receiving the instruction to play back audio content, (i) retrieving, via an I/O interface, the audio content from an audio source that is remote from the playback device and (ii) playing back the retrieved audio content via the audio stage and the one or more speakers; while playing back the retrieved audio content via the audio stage and the one or more speakers, receiving, via the network interface from the first control device, a message indicating that first headphones are connected to the first control device of the media playback system; and in response to receiving the message indicating that the first headphones are connected to the first control device of the media playback system: (i) stopping playback of the retrieved audio content via the audio stage and the one or more speakers and (ii) causing, via the network interface, the first control device to play back the audio content via the first headphones. 
     While some examples described herein may refer to functions performed by given actors such as “users” and/or other entities, it should be understood that this description is for purposes of explanation only. The claims should not be interpreted to require action by any such example actor unless explicitly required by the language of the claims themselves. 
     Moreover, some functions are described herein as being performed “based on” or “in response to” another element or function. For the sake of brevity, functions are generally described as being based on another function when a functional link exists; however, disclosure of “based on” or “in response to” should be understood as disclosing either type of functional relationship. In the claims, “based on” should be understood that one element or function is related to another function or element and “in response to” should be understood as one element or function being a necessary result of another function or element. 
     II. Example Operating Environment 
       FIG.  1    illustrates an example configuration of a media playback system  100  in which one or more embodiments disclosed herein may be implemented. The media playback system  100  as shown is associated with an example home environment having several rooms and spaces, such as for example, an office, a dining room, and a living room. Within these rooms and spaces, the media playback system  100  includes playback devices  102  (identified individually as playback devices  102   a - 102   m ) and control devices  103   a  and  103   b  (collectively “control devices  103 ”). In various examples, a pair of headphones  104  may be connected to the control device  103 . 
     The various playback and control devices  102 - 103  and/or other network devices of the media playback system  100  may be coupled to one another via point-to-point connections and/or over other connections, which may be wired and/or wireless, via a LAN including a network router  106 . For example, the playback device  102   j  (designated as “Left”) may have a point-to-point connection with the playback device  102   a  (designated as “Right”). In one embodiment, the Left playback device  102   j  may communicate over the point-to-point connection with the Right playback device  102   a . In a related embodiment, the Left playback device  102   j  may communicate with other network devices via the point-to-point connection and/or other connections via the LAN. 
     The network router  106  may be coupled to one or more remote computing device(s)  105  via a wide area network (WAN)  107 . In some embodiments, the remote computing device(s)  105  may be cloud servers. The remote computing device(s)  105  may be configured to interact with the media playback system  100  in various ways. For example, the remote computing device(s) may be configured to facilitate streaming and controlling playback of media content, such as audio, in the home environment, perhaps as part of providing a streaming audio service via WAN  107 . In some examples, the remote computing device(s)  105  may be representative of cloud servers from multiple services, perhaps operated by different entities. 
     Further aspects relating to the different components of the example media playback system  100  and how the different components may interact to provide a user with a media experience may be found in the following sections. While discussions herein may generally refer to the example media playback system  100 , technologies described herein are not limited to applications within, among other things, the home environment as shown in  FIG.  1   . For instance, the technologies described herein may be useful in other home environment configurations comprising more or fewer of any of the playback and/or control devices  102 - 103 . Additionally, the technologies described herein may be useful in environments where multi-zone audio may be desired, such as, for example, a commercial setting like a restaurant, mall or airport, a vehicle like a sports utility vehicle (SUV), bus or car, a ship or boat, an airplane, and so on. 
     a. Example Playback Devices 
       FIG.  2    is a functional block diagram illustrating certain aspects of a selected one of the playback devices  102  shown in  FIG.  1   . As shown, such a playback device may include a processor  212 , software components  214 , memory  216 , audio processing components  218 , audio amplifier(s)  220 , speaker(s)  222 , microphone(s)  224 , and a network interface  230  including wireless interface(s)  232  and wired interface(s)  234 . In some embodiments, a playback device might not include the speaker(s)  222 , but rather a speaker interface for connecting the playback device to external speakers. In certain embodiments, the playback device may include neither the speaker(s)  222  nor the audio amplifier(s)  222 , but rather an line-out interface for connecting a playback device to an external audio amplifier or audio-visual receiver. The playback device includes a housing  238  carrying its constituent components. 
     A playback device may further include a user interface  226 . The user interface  226  may facilitate user interactions independent of or in conjunction with one or more of the control devices  103 . In various embodiments, the user interface  226  includes one or more of physical buttons and/or graphical user interfaces provided on touch sensitive screen(s) and/or surface(s), among other possibilities, for a user to directly provide input. The user interface  226  may further include one or more of lights and the speaker(s) to provide visual and/or audio feedback to a user. 
     In some embodiments, the processor  212  may be a clock-driven computing component configured to process input data according to instructions stored in the memory  216 . The memory  216  may be a tangible computer-readable medium configured to store instructions executable by the processor  212 . For example, the memory  216  may be data storage that can be loaded with one or more of the software components  214  executable by the processor  212  to achieve certain functions. In one example, the functions may involve a playback device retrieving audio data from an audio source or another playback device. In another example, the functions may involve a playback device sending audio data to another device on a network. In yet another example, the functions may involve pairing of a playback device with one or more other playback devices to create a multi-channel audio environment. 
     Certain functions may involve a playback device synchronizing playback of audio content with one or more other playback devices. During synchronous playback, a listener may not perceive time-delay differences between playback of the audio content by the synchronized playback devices. U.S. Pat. No. 8,234,395 filed Apr. 4, 2004, and titled “System and method for synchronizing operations among a plurality of independently clocked digital data processing devices,” which is hereby incorporated by reference in its entirety, provides in more detail some examples for audio playback synchronization among playback devices. 
     The audio processing components  218  may include one or more digital-to-analog converters (DAC), an audio preprocessing component, an audio enhancement component or a digital signal processor (DSP), and so on. In some embodiments, one or more of the audio processing components  218  may be a subcomponent of the processor  212 . In one example, audio content may be processed and/or intentionally altered by the audio processing components  218  to produce audio signals. The produced audio signals may then be provided to the audio amplifier(s)  210  for amplification and playback through speaker(s)  212 . Particularly, the audio amplifier(s)  210  may include devices configured to amplify audio signals to a level for driving one or more of the speakers  212 . The speaker(s)  212  may include an individual transducer (e.g., a “driver”) or a complete speaker system involving an enclosure with one or more drivers. A particular driver of the speaker(s)  212  may include, for example, a subwoofer (e.g., for low frequencies), a mid-range driver (e.g., for middle frequencies), and/or a tweeter (e.g., for high frequencies). In some cases, each transducer in the one or more speakers  212  may be driven by an individual corresponding audio amplifier of the audio amplifier(s)  210 . In addition to producing analog signals for playback, the audio processing components  208  may be configured to process audio content to be sent to one or more other playback devices for playback. 
     Audio content to be processed and/or played back by a playback device may be received from an external source, such as via an audio line-in input connection (e.g., an auto-detecting 3.5 mm audio line-in connection) or the network interface  230 . 
     The network interface  230  may be configured to facilitate a data flow between a playback device and one or more other devices on a data network. As such, a playback device may be configured to receive audio content over the data network from one or more other playback devices in communication with a playback device, network devices within a local area network, or audio content sources over a wide area network such as the Internet. In one example, the audio content and other signals transmitted and received by a playback device may be transmitted in the form of digital packet data containing an Internet Protocol (IP)-based source address and IP-based destination addresses. In such a case, the network interface  230  may be configured to parse the digital packet data such that the data destined for a playback device is properly received and processed by the playback device. 
     As shown, the network interface  230  may include wireless interface(s)  232  and wired interface(s)  234 . The wireless interface(s)  232  may provide network interface functions for a playback device to wirelessly communicate with other devices (e.g., other playback device(s), speaker(s), receiver(s), network device(s), control device(s) within a data network the playback device is associated with) in accordance with a communication protocol (e.g., any wireless standard including IEEE 802.11a, 802.11b, 802.11g, 802.11n, 802.11ac, 802.15, 4G mobile communication standard, and so on). The wired interface(s)  234  may provide network interface functions for a playback device to communicate over a wired connection with other devices in accordance with a communication protocol (e.g., IEEE 802.3). While the network interface  230  shown in  FIG.  2    includes both wireless interface(s)  232  and wired interface(s)  234 , the network interface  230  might include only wireless interface(s) or only wired interface(s) in various examples. 
     By way of illustration, SONOS, Inc. presently offers (or has offered) for sale certain playback devices including a “PLAY:1,” “PLAY:3,” “PLAY:5,” “PLAYBAR,” “CONNECT:AMP,” “CONNECT,” and “SUB.” Any other past, present, and/or future playback devices may additionally or alternatively be used to implement the playback devices of example embodiments disclosed herein. Additionally, it is understood that a playback device is not limited to the example illustrated in  FIG.  2    or to the SONOS product offerings. For example, a playback device may include a wired or wireless headphone. In another example, a playback device may include or interact with a docking station for personal mobile media playback devices. In yet another example, a playback device may be integral to another device or component such as a television, a lighting fixture, or some other device for indoor or outdoor use. 
     b. Example Playback Zone Configurations 
     Referring back to the media playback system  100  of  FIG.  1   , the environment may have one or more playback zones, each with one or more playback devices. The media playback system  100  may be established with one or more playback zones, after which one or more zones may be added, or removed to arrive at the example configuration shown in  FIG.  1   . Each zone may be given a name according to a different room or space such as an office, bathroom, master bedroom, bedroom, kitchen, dining room, living room, and/or balcony. In one case, a single playback zone may include multiple rooms or spaces. In another case, a single room or space may include multiple playback zones. 
     As shown in  FIG.  1   , the balcony, dining room, kitchen, bathroom, office, and bedroom zones each have one playback device, while the living room and master bedroom zones each have multiple playback devices. In the living room zone, playback devices  102   a ,  102   b ,  102   j , and  102   k  may be configured to play audio content in synchrony as individual playback devices, as one or more bonded playback devices, as one or more consolidated playback devices, or any combination thereof. Similarly, in the case of the master bedroom, playback devices  102   f  and  102   g  may be configured to play audio content in synchrony as individual playback devices, as a bonded playback device, or as a consolidated playback device. 
     In one example, one or more playback zones in the environment of  FIG.  1    may each be playing different audio content. For instance, the user may be grilling in the balcony zone and listening to hip hop music being played by the playback device  102   c  while another user may be preparing food in the kitchen zone and listening to classical music being played by the playback device  102   i . In another example, a playback zone may play the same audio content in synchrony with another playback zone. For instance, the user may be in the office zone where the playback device  102   d  is playing the same rock music that is being playing by playback device  102   c  in the balcony zone. In such a case, playback devices  102   c  and  102   d  may be playing the rock music in synchrony such that the user may seamlessly (or at least substantially seamlessly) enjoy the audio content that is being played out-loud while moving between different playback zones. Synchronization among playback zones may be achieved in a manner similar to that of synchronization among playback devices, as described in previously referenced U.S. Pat. No. 8,234,395. 
     As suggested above, the zone configurations of the media playback system  100  may be dynamically modified, and in some embodiments, the media playback system  100  supports numerous configurations. For instance, if a user physically moves one or more playback devices to or from a zone, the media playback system  100  may be reconfigured to accommodate the change(s). For instance, if the user physically moves the playback device  102   c  from the balcony zone to the office zone, the office zone may now include both the playback device  102   d  and the playback device  102   c . The playback device  102  may be paired or grouped with the office zone and/or renamed if so desired via a control device such as the control devices  103   a  and  103   b . On the other hand, if the one or more playback devices are moved to a particular area in the home environment that is not already a playback zone, a new playback zone may be created for the particular area. 
     Further, different playback zones of the media playback system  100  may be dynamically combined into zone groups or split up into individual playback zones. For instance, the dining room zone and the kitchen zone may be combined into a zone group for a dinner party such that playback devices  102   i  and  102   l  may render audio content in synchrony. On the other hand, the living room zone may be split into a television zone including playback device  102   b , and a listening zone including playback devices  102   a ,  102   j , and  102   k , if the user wishes to listen to music in the living room space while another user wishes to watch the television  108 . 
     In some implementations, the playback devices  102  of media playback system  100  may be arranged into a smart home hierarchy referred to as Home Graph. The base unit of the home graph hierarchy is a “Set.” For the purpose of this disclosure, a “Set” refers to an individual device or multiple devices that operate together in performing a given function. For instance, a bonded zone of audio playback devices (e.g., a stereo pair or surround sound configuration) function together in playing back audio content by playing back respective channels or portions of that content. As another example, multiple smart lightbulbs in the same light fixture function together in providing illumination from that light fixture. To individually control different smart devices, each of these smart devices may be assigned into a respective Set. 
     The next level of the Home Graph hierarchy is a “Room.” Under the example home graph hierarchy described herein, a “Room” can be considered a container for Sets in a given room of a home. For example, an example Room might correspond to the kitchen of a home, and be assigned the name “Kitchen.” The afore-mentioned Sets having the names “Kitchen Island” and “Kitchen Lights” may belong to the Room. 
     Under home graph, Sets within the room container may be referred to by the name of the room. For instance, the voice command “Play music in Kitchen” causes the “Kitchen Island” Set (which includes an audio playback device) to start playing music. If there are multiple Sets in the Kitchen that include audio playback devices, the voice command “Play music in Kitchen” invokes every Set in the “Kitchen” Room that includes an audio playback device. If control of an individual Set is desired, that Set may be selected by reference to its name (e.g., “Kitchen Island”) rather than the name of the Room. 
     The next level of the example home graph hierarchy is “Area.” Many homes are naturally divided into areas, such as upstairs and downstairs. Under a first example implementation of home graph, an Area includes two or more rooms. For instance, a user may pre-define two Areas named “upstairs” and “downstairs,” which include the Rooms upstairs and the Rooms downstairs in the home, respectively. Under a second example, an area contains two or more sets (possibly in different Rooms). 
     The highest level of the home graph hierarchy is “Home.” A Home refers to the entire home, and all of the Sets within. In some implementations, the Home may be referred to by reference to “everywhere.” For the purposes of this disclosure, the terms “Set,” “Room,” “Area” and “Home” are capitalized when referring to levels of the home graph hierarchy so as to distinguish from the common usage of these terms. Moreover, human-readable names (i.e., character strings) are used in identifying Sets, Rooms, Areas, and Home and are denoted by quotations marks (e.g., “Nick&#39;s Room” Set). 
     c. Example Control Devices 
       FIG.  3    is a functional block diagram illustrating certain aspects of a selected one of the controller devices  103  of the media playback system  100  of  FIG.  1   . Such controller devices may also be referred to as a controller or a control device. The controller device shown in  FIG.  3    may include components that are generally similar to certain components of the network devices described above, such as a processor  312 , memory  316 , and a network interface  330 . In one example, a controller device may be a dedicated controller for the media playback system  100 . In another example, a controller device may be a network device on which media playback system controller application software may be installed, such as for example, an iPhone™, iPad™ or any other smart phone, tablet or network device (e.g., a networked computer such as a PC or Mac™). The control device  103  includes a housing  338  carrying its constituent components. 
     The memory  316  of the control device  103  may be configured to store controller application software and other data associated with the media playback system  100  and a user of the system  100 . The memory  316  may be loaded with one or more software components  314  executable by the processor  312  to achieve certain functions, such as facilitating user access, control, and configuration of the media playback system  100 . The control device  103  communicates with other network devices over the network interface  330 , such as a wireless interface, as described above. 
     The control device  103  may include a plurality of microphones arranged to detect sound in the environment of the control device  103 . The microphones may detect voice inputs to the media playback system  100 , process those inputs, perhaps using one or more VASs, and carry out the commands on one or more playback devices  102 . 
     Playback device control commands such as volume control and audio playback control may also be communicated from a control device to a playback device via the network interface  330 . As suggested above, changes to configurations of the media playback system  100  may also be performed by a user using the control device. The configuration changes may include adding/removing one or more playback devices to/from a zone, adding/removing one or more zones to/from a zone group, forming a bonded or merged player, separating one or more playback devices from a bonded or merged player, among others. 
     In one example, data and information (e.g., such as a state variable) may be communicated between a control device and other devices via the network interface  330 . For instance, playback zone and zone group configurations in the media playback system  100  may be received by a control device from a playback device, another control device, or another network device, or transmitted by the control device to another playback device or control device via the network interface  330 . In some cases, the other network device may be another control device. 
     The headphone interface(s)  336  may include analog interface(s)  338  and/or wireless interface(s)  340 . The analog interface(s)  338  may include a headphone jack (also known as a phone connector) in 2.5 mm or 3.5 mm connectors, among other examples. Such a headphone jack connects to an audio chipset of the control device  300 , which may be integrated into the processor  312  for instance, perhaps as part of a system-on-a-chip (SOC). Output from the audio chipset is provided to headphones connected to the analog interface(s)  338  to drive the headphones in producing audio output. The wireless interface(s)  340  may include a personal area network (PAN) network interface that supports a standard such as Bluetooth® SIG (formally standardized as IEEE 802.15.1). Via the wireless interface(s)  340 , the control device  300  may form a wireless point-to-point connection with compatible headphones to provide audio to the headphones for playback. 
     Control device  300  may maintain a state variable indicating whether headphones are connected to the headphone interface(s)  336 . In particular, connection or disconnection of headphones to analog interface(s)  338  may complete or disconnect a circuit (e.g., a circuit including the amplifier output of the audio chipset), which in turn triggers updating of the state variable to indicate whether headphones are connected. As another example, when headphones are connected to the wireless interface(s)  340 , a headset-specific profile, such as Advanced Audio Distribution Profile (A2DP) may be used. Use of the A2DP profile with a Bluetooth® compatible device may cause the state variable to indicate that headphones are connected. Other examples are possible as well. 
     The user interface(s)  326  of a control device may be configured to facilitate user access and control of the media playback system  100 , by providing controller interface(s) such as the controller interfaces  326   a  and  326   b  shown in  FIGS.  4 A and  4 B , respectively, which may be referred to collectively as the controller interface  326 . Referring to  FIGS.  4 A and  4 B  together, the controller interface  326  includes a playback control region  442 , a playback zone region  443 , a playback status region  444 , a playback queue region  446 , and a sources region  448 . The user interface  326  as shown is just one example of a user interface that may be provided on a network device such as the control device shown in  FIG.  3    and accessed by users to control a media playback system such as the media playback system  100 . Other user interfaces of varying formats, styles, and interactive sequences may alternatively be implemented on one or more network devices to provide comparable control access to a media playback system. 
     The playback control region  442  ( FIG.  4 A ) may include selectable (e.g., by way of touch or by using a cursor) icons to cause playback devices in a selected playback zone or zone group to play or pause, fast forward, rewind, skip to next, skip to previous, enter/exit shuffle mode, enter/exit repeat mode, enter/exit cross fade mode. The playback control region  442  may also include selectable icons to modify equalization settings, and playback volume, among other possibilities. 
     The playback zone region  443  ( FIG.  4 B ) may include representations of playback zones within the media playback system  100 . The playback zones regions may also include representation of zone groups, such as the Dining Room+Kitchen zone group, as shown. In some embodiments, the graphical representations of playback zones may be selectable to bring up additional selectable icons to manage or configure the playback zones in the media playback system, such as a creation of bonded zones, creation of zone groups, separation of zone groups, and renaming of zone groups, among other possibilities. 
     For example, as shown, a “group” icon may be provided within each of the graphical representations of playback zones. The “group” icon provided within a graphical representation of a particular zone may be selectable to bring up options to select one or more other zones in the media playback system to be grouped with the particular zone. Once grouped, playback devices in the zones that have been grouped with the particular zone will be configured to play audio content in synchrony with the playback device(s) in the particular zone. Analogously, a “group” icon may be provided within a graphical representation of a zone group. In this case, the “group” icon may be selectable to bring up options to deselect one or more zones in the zone group to be removed from the zone group. Other interactions and implementations for grouping and ungrouping zones via a user interface such as the user interface  326  are also possible. The representations of playback zones in the playback zone region  443  ( FIG.  4 B ) may be dynamically updated as playback zone or zone group configurations are modified. 
     The playback status region  444  ( FIG.  4 A ) may include graphical representations of audio content that is presently being played, previously played, or scheduled to play next in the selected playback zone or zone group. The selected playback zone or zone group may be visually distinguished on the user interface, such as within the playback zone region  443  and/or the playback status region  444 . The graphical representations may include track title, artist name, album name, album year, track length, and other relevant information that may be useful for the user to know when controlling the media playback system via the user interface  426 . 
     The playback queue region  446  may include graphical representations of audio content in a playback queue associated with the selected playback zone or zone group. In some embodiments, each playback zone or zone group may be associated with a playback queue containing information corresponding to zero or more audio items for playback by the playback zone or zone group. For instance, each audio item in the playback queue may comprise a uniform resource identifier (URI), a uniform resource locator (URL) or some other identifier that may be used by a playback device in the playback zone or zone group to find and/or retrieve the audio item from a local audio content source or a networked audio content source, possibly for playback by the playback device. 
     In one example, a playlist may be added to a playback queue, in which case information corresponding to each audio item in the playlist may be added to the playback queue. In another example, audio items in a playback queue may be saved as a playlist. In a further example, a playback queue may be empty, or populated but “not in use” when the playback zone or zone group is playing continuously streaming audio content, such as Internet radio that may continue to play until otherwise stopped, rather than discrete audio items that have playback durations. In an alternative embodiment, a playback queue can include Internet radio and/or other streaming audio content items and be “in use” when the playback zone or zone group is playing those items. Other examples are also possible. 
     When playback zones or zone groups are “grouped” or “ungrouped,” playback queues associated with the affected playback zones or zone groups may be cleared or re-associated. For example, if a first playback zone including a first playback queue is grouped with a second playback zone including a second playback queue, the established zone group may have an associated playback queue that is initially empty, that contains audio items from the first playback queue (such as if the second playback zone was added to the first playback zone), that contains audio items from the second playback queue (such as if the first playback zone was added to the second playback zone), or a combination of audio items from both the first and second playback queues. Subsequently, if the established zone group is ungrouped, the resulting first playback zone may be re-associated with the previous first playback queue, or be associated with a new playback queue that is empty or contains audio items from the playback queue associated with the established zone group before the established zone group was ungrouped. Similarly, the resulting second playback zone may be re-associated with the previous second playback queue, or be associated with a new playback queue that is empty, or contains audio items from the playback queue associated with the established zone group before the established zone group was ungrouped. Other examples are also possible. 
     With reference still to  FIGS.  4 A and  4 B , the graphical representations of audio content in the playback queue region  446  ( FIG.  4 B ) may include track titles, artist names, track lengths, and other relevant information associated with the audio content in the playback queue. In one example, graphical representations of audio content may be selectable to bring up additional selectable icons to manage and/or manipulate the playback queue and/or audio content represented in the playback queue. For instance, a represented audio content may be removed from the playback queue, moved to a different position within the playback queue, or selected to be played immediately, or after any currently playing audio content, among other possibilities. A playback queue associated with a playback zone or zone group may be stored in a memory on one or more playback devices in the playback zone or zone group, on a playback device that is not in the playback zone or zone group, and/or some other designated device. Playback of such a playback queue may involve one or more playback devices playing back media items of the queue, perhaps in sequential or random order. 
     d. Example Audio Content Sources 
     The sources region  448  ( FIG.  4 A ) may include graphical representations of selectable audio content sources and voice assistant services (VAS). The audio sources in the sources region  348  may be audio content sources from which audio content may be retrieved and played by the selected playback zone or zone group. One or more playback devices in a zone or zone group may be configured to retrieve for playback audio content (e.g., according to a corresponding uniform resource identifier (URI) or uniform resource locator (URL) for the audio content) from a variety of available audio content sources. In one example, audio content may be retrieved by a playback device directly from a corresponding audio content source (e.g., a line-in connection). In another example, audio content may be provided to a playback device over a network via one or more other playback devices or network devices. 
     Example audio content sources may include a memory of one or more playback devices in a media playback system such as the media playback system  100  of  FIG.  1   , local music libraries on one or more network devices (such as a control device, a network-enabled personal computer, or a networked-attached storage (NAS), for example), streaming audio services providing audio content via the Internet (e.g., the cloud), or audio sources connected to the media playback system via a line-in input connection on a playback device or network devise, among other possibilities. 
     In some embodiments, audio content sources may be regularly added or removed from a media playback system such as the media playback system  100  of  FIG.  1   . In one example, an indexing of audio items may be performed whenever one or more audio content sources are added, removed or updated. Indexing of audio items may involve scanning for identifiable audio items in all folders/directory shared over a network accessible by playback devices in the media playback system, and generating or updating an audio content database containing metadata (e.g., title, artist, album, track length, among others) and other associated information, such as a URI or URL for each identifiable audio item found. Other examples for managing and maintaining audio content sources may also be possible. 
     III. Example Headphone Interactions 
       FIG.  5 A  illustrates an example configuration of a system in which example headphone interactions may be practiced. As shown, the system of  FIG.  5 A  includes the playback device  102   l  of media playback system  100 , a control device  103 , headphones  104 , and a network router  106 . In operation, connection of the headphones  104  to the control device  103  causes the control device  103  to transition playback of audio content from the playback device  102   l  to the control device  103  (via the headphones  104 ). Similarly, disconnection of the headphones  104  from the control device  103  causes the control device  103  to transition playback of audio content from the control device  103  (via the headphones  104 ) to the playback device  102   l.    
     In  FIG.  5 A , the playback device  102   l  and the control device  103  are connected via the router  106 . In alternative implementations, these devices may directly connect via a point-to-point network such as an ad-hoc WiFi® network or a Bluetooth® connection. Other types of connections that facilitate exchange of instructions and/or content may be implemented as well. 
     To illustrate example headphone interactions,  FIG.  5 B  is a message flow diagram  550  showing instructions exchanged between the control device  103 , the playback device  102   l , and the remote computing devices  105  (i.e., a content server of a streaming audio service). Such messages are representative and example implementations that use additional or fewer messages are contemplated. 
     At  551 , the control device  103  sends a message to the playback device  102   l  that instructs the playback device  102   l  to add particular audio content to the queue of playback device  102   l  for playback. The message includes a URI indicating the location of the audio content at the remote computing devices  105 . The message also instructs the playback device  102   l  to play back the queue. In other examples, separate messages may instruct the playback device  102   l  to add the audio content to the queue and to play back the queue. 
     In an example, the control device  103  may send such a message based on receiving user input indicating an instruction to play back audio content on playback device  102   l . For instance, via user interface  326 , one or more audio tracks, Internet radio stations, or other audio content is selected for playback on playback device  102   l , which as shown in  FIG.  1    is configured as the Dining Room zone (which can also be referred to as the Dining Room “Room”). Such user input may involve a selection of the Dining Room zone (or perhaps a selection of a zone group that includes the Office zone) and selection of audio content to add to a queue of the Office zone (or of the zone group that includes the Office Zone). For instance, as shown in  FIG.  4 B , the user may select the “Dining Room+Kitchen” zone group in the playback zone region  443  of user interface  326   b . In further examples, the input may involve selection of a Set, Room, Area, or Home of the Home Graph hierarchy described above. 
     Based on receiving the message instructing the playback device  102   l  to add an audio content to the queue of playback device  102   l  for playback, at  552 , the playback device  102   l  sends a fetch message to the remote computing devices  105  requesting the audio content at the URI. Based on this fetch message, at  553 , the remote computing devices  105  stream the audio content to the playback device  102   l . The playback device  102   l  receives the audio content stream and plays back the audio content. At  554 , the playback device  102   l  provides its status back to the control device  103  via a state variable indicating that the playback device  102   l  is playing back the audio content. 
     In an example in which playback device  102   l  is joined into a zone group (e.g., the “Dining Room+Kitchen” zone group), the playback device  102   l  and other playback devices of the zone group (e.g., the playback device  102   i  of the Kitchen zone), play back the audio content in synchrony. In such an example, the playback device  102   l  may operate as a zone group coordinator for the zone group by distributing the audio content stream and timing information to the other playback devices in the zone group via the network provided by network router  106  to facilitate synchronous playback, as described in previously referenced U.S. Pat. No. 8,234,395. 
     While the playback device  102   l  is playing back the audio content, at  555 , the control device  103  detects connection of the headphones  104  to the control device  103 . As described above in connection with  FIG.  3   , the control device  103  includes headphone interface(s)  336  to facilitate connection of the headphones  104  to the control device  103 . Detecting connection of the headphones  104  may involve detecting a change in status of a state variable that is maintained by the headphone interface(s)  336 , which indicates whether any headphones  104  are connected to the control device  103  via headphone interface(s)  336 . 
     Based on detecting connection of the headphones  104  to the control device  103 , the control device  103  transitions playback of the audio content from the playback device  102   l  to the control device  103 . More particularly, the control device stops playback on the playback device  1021  at a given play position and starts playback of the audio content on the control device  103  at the same play position. These operations effectively transition playback of the audio content from the playback device  102   l  to the control device  103 . 
     To stop playback on the playback device  102 , at  556 , the control device  103  sends a message that instructs the playback device  102   l  to stop playback. In some examples, this message instructs the playback device to mute the audio content playback, which effectively stops playback from the perspective of the user. Muting the audio content playback (rather than stopping it completely) may facilitate transitioning playback back to the playback device  102   l  as the playback merely needs to be unmuted. However, such an implementation may use additional network resources (from streaming the audio content) and prevent the playback device  102   l  from going into certain low-power modes. As such, in alternate examples, the message instructs the playback device  102   l  to stop playback. 
     If playback device  102   l  is configured into a bonded zone, zone group, or other synchrony group, the control device  103  stops playback on all the playback devices in the synchrony group. In one example, the control device  103  sends the message that instructs the playback device  102   l  to stop playback to playback device  102   l  and, based on this message, playback device  102   l  instructs the other playback device(s) of the synchrony group to stop playback. Alternatively, the control device  103  sends messages to the playback devices of the synchrony group to instruct the playback devices to stop playback. 
     In some examples, the control device  103  receives an offset indicating a current play position of the audio content. The control device  103  may receive this offset based on the message instructing the playback device  102   l  to stop playback or a message requesting the offset, among other examples. In other examples, the play position is tracked by the control device  103  so as to facilitate showing an indication of play position on the control interface  326 . In such examples, the playback device  102   l  may share the play position with the control device  103  as a state variable to facilitate accuracy of the play position indicator and to facilitate the example headphone interactions disclosed herein. 
     To start playback on the control device  103 , at  557 , the control device  103  sends a fetch message to the remote content servers  105  requesting the audio content at the URI. The fetch message may include an offset indicating the current play position of the audio content so as to instruct the remote content servers  105  to stream the audio content beginning with that play position. Based on this fetch message, at  558 , the remote computing devices  105  stream the audio content to the control device  103 . The control device  103  receives the audio content stream and plays back the audio content via the headphones  104 . 
     In another example, the headphones  104  may already be connected to the control device  103  when the control device  103  receives an instruction to play audio content on a given playback device, bonded zone, zone group, or Home Graph hierarchy target (e.g., a Room or Area). In such examples, the control device  103  might not perform the steps at  551 - 544 . Instead, the process may begin with performing the detect connection of headphones step shown at  555  and based on detecting that the headphones are connected, the control device  103  sends a fetch message to the remote content servers  105  requesting the audio content at the URI. Based on this fetch message, the remote computing devices  105  stream the audio content to the control device  103 . The control device  103  receives the audio content stream and plays back the audio content via the headphones  104 . 
     In some implementations, certain types of playback devices  102  are headphone-enabled. Before transitioning playback from a given playback device  102  to headphones  104  connected to the control device  103 , the control device  103  may determine whether the given playback device  102  is headphone-enabled. Determining whether the given playback device  102  is headphone-enabled may involve checking a state variable maintained within the media playback system  100  that indicates whether given playback device  102  is headphone-enabled. In such implementations, if the given playback device  102  is headphone enabled, the control device  103  proceeds with transitioning playback. If not, the control device  103  does not transition playback. 
     Designating certain types of devices as headphone-enabled (or headphone-disabled) may prevent unexpected behavior in a multi-zone multi-controller system such as media playback system  100 . Video-associated playback devices (i.e., playback devices, such as soundbar-type devices that are configured to play back audio in synchrony with video playing on a television) are an example type or category of playback devices that can be designated as headphone-enabled (or disabled) in various implementations. Grouped playback devices (e.g. playback devices  102  in a zone group or Area) are another example type or category of playback devices that can be designated as headphone-enabled (or disabled) in various implementations. Other examples are possible as well. 
     In some implementations, a given playback device  102  (or a given zone group, Area, or other group) becomes headphone-disabled when a first control device  103  has transitioned playback from the given playback device  102  to playback on the first control device  103  with headphones  104 . This configuration prevents a second control device  103  from transitioning playback from the given playback device  102  to playback on the second control device  103 , effectively limiting the feature to one set of headphones  104 . Such a configuration may prevent unexpected behavior in a multi-zone multi-controller system such as media playback system  100 . 
     To illustrate a further example,  FIG.  5 C  is a message flow diagram  560  showing instructions exchanged between the control device  103 , the playback device  102   l , and the remote computing devices  105  (i.e., a content server of a streaming audio service) to transition playback back from the control device  103  to the playback device  102   l . Such messages are representative and example implementations that use additional or fewer messages are contemplated. 
     At  561 , the remote computing devices  105  are streaming audio content to the control device  103 , which plays the audio content back via headphones  104 . Such a step is akin to the streaming performed at step  558  of  FIG.  5 B  based on the fetch request at  557  to facilitate transferring playback from the playback device  102   l  to the control device  103 . Alternatively, the control device  103  may send a fetch request based on audio content being selected for playback on the control device  103 . 
     While the control device  103  is playing back the audio content via headphones  104 , at  562 , the control device  103  detects disconnection of the headphones  104  from the control device  103 . As described above in connection with  FIG.  3   , the control device  103  includes headphone interface(s)  336  to facilitate connection of the headphones  104  to the control device  103 . Detecting disconnection of the headphones  104  may involve detecting a change in status of a state variable that is maintained by the headphone interface(s)  336 , which indicates whether any headphones  104  are connected to the control device  103  via headphone interface(s)  336 . 
     Based on detecting disconnection of the headphones  104  from the control device  103 , the control device  103  transitions playback of the audio content from the control device  103  to the playback device  102   l . More particularly, the control device stops playback on the control device  103  at a given play position and starts playback of the audio content on the playback device  102   l  at the same play position. These operations effectively transition playback of the audio content from the control device  103  to the playback device  102   l.    
     At  563 , the control device  103  sends a message to the playback device  102   l  that instructs the playback device  102   l  to add particular audio content to the queue of playback device  102   l  for playback. The message includes a URI indicating the location of the audio content at the remote computing devices  105 . The message also instructs the playback device  102   l  to play back the queue. In other examples, separate messages may instruct the playback device  102   l  to add the audio content to the queue and to play back the queue. In some examples, the message includes an offset indicating a current play position of the audio content. 
     Based on receiving the message instructing the playback device  102   l  to add an audio content to the queue of playback device  102   l  for playback, at  552 , the playback device  102   l  sends a fetch message to the remote computing devices  105  requesting the audio content at the URI. Based on this fetch message, at  553 , the remote computing devices  105  stream the audio content to the playback device  102   l . The playback device  102   l  receives the audio content stream and plays back the audio content. 
     Alternatively, if playback by playback device  102   l  was stopped via muting, the message may instruct the playback device  102   l  to unmute the playback, which, in combination with stopping playback on the control device  103  with the headphones  104 , effectively transitions playback back to the playback device  102   l . In such examples, the fetch message from the playback device  102   l  is unnecessary, as the playback device  102   l  is already streaming the audio content. 
     In some implementations, when the control device  103  detects that the headphones  104  are disconnected (or otherwise disabled), the control device  103  verifies that the user has indicated that playback should be transitioned in such circumstances. For instance, the control device  103  may display a selectable control prompting the user to confirm that playback should resume on the playback device  102   l . When the selectable control is selected, the control device  103  transitions playback to the playback device  102   l . Alternatively, verification may be pre-set in advance using a policy. 
     To illustrate such a prompt,  FIG.  6 A  shows a controller interface  326   c  displayed on control device  103 . As shown, controller interface  326   c  includes a prompt  671  indicating the control device  103  detected that the headphones  104  were disconnected from the control device  103 . Controller interface  326   c  also includes a selectable control  672  that, when selected, causes the control device  103  to transition playback to playback device  102   l  (in the Dining Room zone). Alternatively, selectable controls  673  and  674  cause the control device  103  to continue playing back the audio content on the control device  103  (e.g., via integrated speakers) or to stop playback entirely, respectively. As indicated above, the controller interface  326   c  may additionally display selectable controls to optionally adjust a playback volume when playback resumes on playback device  102   l.    
     To illustrate example policies,  FIG.  6 B  shows a controller interface  326   d  displayed on control device  103 . As shown, controller interface  326   d  includes a policy region  676  that includes slider controls  677   a - e . Each slider control  677   a - e  allows setting of a policy for a respective zone. In particular, each slider control  677   a - e  is controllable via touch input to set the hours (i.e., portions of a 24 hour cycle) for automatically transitioning playback for a respective zone, as shown. Additional slider controls (e.g., for other zones of a media playback system) may be accessed by scrolling the policy region  676 . While zones are shown by way of example, polices may be set for various groupings, such as zone groups or Areas as well. 
     Turning to another example,  FIG.  7 A  illustrates another example configuration of a system in which example headphone interactions may be practiced. As shown, the system of  FIG.  7 A  includes the playback device  102   b  of media playback system  100  (i.e., a soundbar-type device), the control device  103 , headphones  104 , and a network router  106 . In operation, connection of the headphones  104  to the control device  103  causes the control device  103  to transition playback of audio content from the playback device  102   b  to the control device  103  (via the headphones  104 ). Similarly, disconnection of the headphones  104  from the control device  103  causes the control device  103  to transition playback of audio content from the control device  103  (via the headphones  104 ) to the playback device  102   l.    
     In an example, playback device  102   b  is configured to receive audio content from television  780  and play back that audio content in synchrony with video playing on the television  780  (i.e., to play back the television audio). In such a configuration, when playback is transitioned from the playback device  102   b  to the control device  103  (via the headphones  104 ), playback device  102   b  may provide the audio content to the control device  103 . Moreover, to keep the audio content playback in synchrony with the video content playing on the television  108 , playback device  102   b  and control device  103  form a synchrony group in which playback device  102   b  provides audio content and timing information to control device  102   b.    
     To illustrate,  FIG.  7 B  is a message flow diagram  780  showing instructions exchanged between the control device  103  and the playback device  102   b . Such messages are representative and example implementations that use additional or fewer messages are contemplated. 
     At  781 , the control device  103  sends a message to the playback device  102   b  that instructs the playback device  102   b  to play back the line-in input (e.g., an HDMI, optical digital or analog input). Based on this instruction, the playback device  102   b  begins playing audio content provided via the line-in connection. At  782 , the playback device  102   b  provides its status back to the control device  103  via a state variable indicating that the playback device  102   l  is playing back audio content from the line-in connection. 
     While the playback device  102   b  is playing back the audio content, at  783 , the control device  103  detects connection of the headphones  104  to the control device  103 . As described above in connection with  FIG.  3   , the control device  103  includes headphone interface(s)  336  to facilitate connection of the headphones  104  to the control device  103 . Detecting connection of the headphones  104  may involve detecting a change in status of a state variable that is maintained by the headphone interface(s)  336 , which indicates whether any headphones  104  are connected to the control device  103  via headphone interface(s)  336 . 
     Based on detecting connection of the headphones  104  to the control device  103 , the control device  103  transitions playback of the audio content from the playback device  102   b  to the control device  103 . More particularly, the control device stops playback on the playback device  102   b  and starts playback of the audio content on the control device  103 . These operations effectively transition playback of the audio content from the playback device  102   b  to the control device  103 . 
     To stop playback on the playback device  102   b , at  784 , the control device  103  sends a message that instructs the playback device  102   b  to mute playback. If playback device  102   b  is configured into a bonded zone, zone group, or other synchrony group, all the playback devices in the synchrony group mute playback as well. For instance, if playback device  102   b  is configured into a bonded zone (i.e., a surround sound configuration) with playback devices  102   a ,  102   j , and  102   k , the message mutes playback on each device in the bonded zone configuration. In one example, the control device  103  sends the message that instructs the playback device  102   b  to mute playback to playback device  102   b  and, based on this message, the playback device  102   b  instructs the other playback device(s) of the synchrony group to mute playback. Alternatively, the control device  103  sends messages to the playback devices of the synchrony group to instruct the playback devices to mute playback. 
     To start playback on the control device  103 , at  785 , the control device  103  sends a message that instructs the playback device  102   b  to form a synchrony group with the control device  103 . Based on this message, the playback device  102   b  forms a synchrony group with the control device  103 . In some examples, the playback device  102   b  becomes a group coordinator of the new synchrony group. As group coordinator, the playback device  102   b  provides audio content and timing information to the control device  103 , as described in previously referenced U.S. Pat. No. 8,234,395. At  786 , the playback device  102   b  streams this audio content and timing information to the control device  103 . 
     In this example, the control device  103  and the playback device  102   b  are playing back the audio content from the television  108  in synchrony. However, playback has effectively transitioned from the playback device  102   b  to the control device  103  since playback on the playback device  102   b  is muted and the control device  103  is now playing back the audio content from the television  108  via the headphones  104 . 
     If the playback device  102   b  was previously in another group, the message at  785  to create a synchrony group may affect this group. In some instances, such as when the group is a synchrony group in which each device plays back the same audio content, the message at  785  causes the control device  103  to join the existing group. In other instances, such as when the group is a bonded zone in which each device plays back the different audio content (e.g., different channels of the audio content), the message at  785  causes formation of a new synchrony group that includes the playback device  102   b  and the control device  103 . 
     During playback on the control device  103 , control inputs received via the control interface  326  may be applied to the synchrony group. Some of these inputs (e.g., volume control) may be only applied to the control device, while others are applied to all devices in the synchrony group (e.g., transport) control. That is, volume control is not reflected on the playback device(s)  102  so that the volume levels of the playback devices  102  are maintained from their pre-muted level. However, transport controls are applied to keep playback in synchrony. 
     To illustrate a further example,  FIG.  7 C  is a message flow diagram  790  showing instructions exchanged between the control device  103  and the playback device  102   b  to transition playback from the control device  103  to the playback device  102   b . Such messages are representative and example implementations that use additional or fewer messages are contemplated. 
     At  791 , the playback device  102   b  is streaming audio content and timing information to the control device  103  to facilitate playback of the audio content from the television  108  via headphones  104 . This step is akin to the streaming performed at step  786  of  FIG.  7 B . 
     While the control device  103  is playing back the audio content via headphones  104 , at  792 , the control device  103  detects disconnection of the headphones  104  from the control device  103 . Based on detecting disconnection of the headphones  104  from the control device  103 , the control device  103  transitions playback of the audio content from the control device  103  to the playback device  102   b . More particularly, the control device  103  stops playback on the control device  103  and starts playback of the audio content on the playback device  102   b . These operations effectively transition playback of the audio content from the control device  103  to the playback device  102   b.    
     At  793 , the control device  103  sends a message to the playback device  102   b  that instructs the playback device  102   b  to dissolve the synchrony group that includes the control device  103 . If the playback device  102   b  was previously part of another synchrony group prior to forming the synchrony group that includes the control device  103 , the playback device  102   b  may re-form that synchrony group (perhaps by removing the control device  103 ). Alternatively, the playback device  102   b  may operate individually. Dissolving the synchrony group that includes the control device  103  stops play back on the control device  103  via the headphones  104 , as this operation causes the playback device  102   b  to stop providing the audio content and timing information to the control device  103 . 
     To start playback of the audio content on the playback device  102   b , the control device  103  sends a message to the playback device  102   b  that instructs the playback device  102   b  to unmute playback. If playback device  102   l  is configured into a bonded zone, zone group, or other synchrony group, all the playback devices in the synchrony group unmute playback as well. For instance, if playback device  102   b  is re-configured into a bonded zone (i.e., a surround sound configuration) with playback devices  102   a ,  102   j , and  102   k , the message unmutes playback on each device in the bonded zone configuration. 
     In some implementations, when the control device  103  detects that the headphones  104  are disconnected (or otherwise disabled), the control device  103  verifies that the user has indicated that playback should be transitioned in such circumstances. For instance, the control device  103  may display a selectable control prompting the user to confirm that playback should resume on the playback device  102   b . The control device  103  may additionally prompt the user to optionally adjust a playback volume when playback resumes on playback device  102   b . Additionally or alternatively, verification may be pre-set in advance using a policy. Examples of such verification are shown in  FIGS.  6 A and  6 B . 
     In further examples, multiple control devices  103  are connectable to the playback device  102  for synchronous playback.  FIG.  7 D  illustrates an example system with two control devices  103  connected to playback device  102   b . Each additional control device  103  is included in the synchrony group that includes the playback device  102  and the first control device. For instance, in  FIG.  7 D , the playback device  102   b  providing audio content and timing information to control devices  103   a  and  103   b  as group coordinator of a synchrony group. 
     In a multiple control device configuration such as  FIG.  7 D , the first control device  103  to detect that headphones are connected may trigger the headphone interaction. For instance, the control device  103   a  may detect that headphones  104   a  were connected to control device  103   a  and transition playback to control device  103   a  via headphones  104   a . Subsequently, the control device  103   b  may detect that headphones  104   b  were connected to control device  103   b  and transition playback to control device  103   b  via headphones  104   b  (e.g., by joining the synchrony group that includes playback device  102   b  and control device  103   a ). 
     At some point thereafter, headphones may be disconnected from one of the control devices. For instance, the control device  103   a  may detect that headphones  104   a  were disconnected from control device  103   a . Based on this detection, the control device  103   a  may leave the synchrony group. However, playback of the audio content from the television  108  continues on to control device  103   b  via headphones  104   b  until control device  103   b  detects that headphones  104   b  were disconnected from control device  103   b . At this point, both control devices  103  leave the synchrony group and audio content playback on playback device  102   b  is unmuted. 
     In some examples, playback devices  102  in proximity to a control device  103  may have their audio playback modified when the control device  103  detects that headphones  104  have been connected or disconnected from the control device  103 . Techniques for determining the location or proximity of a control device relative to a playback device may include or more techniques disclosed in U.S. Pat. No. 9,084,058 filed Dec. 29, 2011, and titled “Sound Field Calibration Using Listener Localization,” which is incorporated herein in its entirety. In addition, techniques for determining the location or proximity of a control device relative to a playback device may include or more techniques disclosed in U.S. Pat. No. 8,965,033 filed Aug. 31, 2012, and titled “Acoustic Optimization” is incorporated herein by reference in its entirety. 
     IV. Example Headphone Interaction Techniques 
     Implementation  1000  shown in  FIG.  8    presents example embodiments of techniques described herein. These example embodiments that can be implemented within an operating environment including, for example, the media playback system  100  of  FIG.  1   , one or more of the playback device  102  of  FIG.  2   , and one or more of the control device  103  of  FIG.  3   , as well as other devices described herein and/or other suitable devices. Further, operations illustrated by way of example as being performed by a media playback system can be performed by any suitable device, such as a playback device or a control device of a media playback system. Implementation  1000  may include one or more operations, functions, or actions as illustrated by one or more of blocks shown in  FIG.  8   . Although the blocks are illustrated in sequential order, these blocks may also be performed in parallel, and/or in a different order than those described herein. Also, the various blocks may be combined into fewer blocks, divided into additional blocks, and/or removed based upon the desired implementation. 
     In addition, for the implementations disclosed herein, the flowcharts show functionality and operation of one possible implementation of present embodiments. In this regard, each block may represent a module, a segment, or a portion of program code, which includes one or more instructions executable by a processor for implementing specific logical functions or steps in the process. The program code may be stored on any type of computer readable medium, for example, such as a storage device including a disk or hard drive. The computer readable medium may include non-transitory computer readable medium, for example, such as computer-readable media that stores data for short periods of time like register memory, processor cache, and Random Access Memory (RAM). The computer readable medium may also include non-transitory media, such as secondary or persistent long term storage, like read only memory (ROM), optical or magnetic disks, compact-disc read only memory (CD-ROM), for example. The computer readable media may also be any other volatile or non-volatile storage systems. The computer readable medium may be considered a computer readable storage medium, for example, or a tangible storage device. In addition, for the implementations disclosed herein, each block may represent circuitry that is wired to perform the specific logical functions in the process. 
     As discussed above, embodiments described herein involve headphone interactions with a media playback system.  FIG.  8    illustrates an example implementation  1000  by which connection and/or disconnection of headphones  104  to a control device  103  of a media playback system  100  may trigger interactions with the media playbacks system  100 . 
     a. Receive Indication of Audio Content 
     At block  1002 , implementation  1000  involves receiving an indication of audio content. In some examples, the control device  103  may receive an indication of audio content may include an indication of audio content that is currently playing on one or more playback devices  102 . Alternatively, the playback device  102  may receive an instruction to play audio content on one or more playback devices  102 , among other examples. 
     For instance, the control device  103  may receive via a network interface, an indication of particular audio content being played back by a first zone of the media playback system. Examples of such indications include the messages indicating state variables at  554  in  FIG.  5 B  and at  782  in  FIG.  7 B . In some instances, the control device  103  may receive such an indication while headphones are disconnected from the first control device. 
     As a further example, the playback device  102  may receive, from a control device  103 , an instruction to play audio content on one or more playback devices  102 . For instance, as shown in  FIG.  5 B  at  551 , the control device  103  may send a message instructing the playback device  102  to play back particular audio content from an audio content URI. Based on such an instruction, the playback device  102  retrieves the audio content from an audio source and plays back the retrieved audio content. 
     b. Detect Connection of Headphones 
     At block  1004 , implementation  1000  involves detecting connection of headphones. For instance, the control device  103  may detect connection of headphones to control device  103 , as discussed at  555  in  FIG.  5 B  and at  783  in  FIG.  7 B . As discussed above, detecting connection of headphones may involve detecting a change in the state of a state variable indicating headphone connection status. Headphones may be connectable to the control device  103  via either an analog headphone jack or a point-to-point personal area network connection via a personal area network interface, among other examples. 
     In another example, detecting connection of headphones involves receiving a message indicating that headphones  104  are connected to the control device  103  of the media playback system. For instance, the playback device  102  may receive such a message from the control device  103  via a network interface based on the control device  103  detecting connection of headphones  104 . In some examples, the playback device  102  may receive such messages from multiple control devices  103  (e.g., from control device  103   a  and control device  103   b  as shown in  FIG.  7 D ). 
     c. Transition Playback From Playback Device(s) To Headphones 
     In  FIG.  10   , at block  1006 , implementation  1000  involves transitioning playback from one or more playback devices to headphones. For instance, the control device  103  may transition playback from the playback device(s)  102  to the control device  103  via headphones  104  based on detecting that the headphones are connected to the control device  103 . In another example, a given playback device  102  may transition playback from the playback device(s)  102  to the control device  103  via headphones  104  based on detecting that the headphones are connected to the control device  103   
     As noted above, the control device  103  may transition playback. Transitioning playback may involve causing the playback device(s)  102  to stop playback of the particular audio content, as described in connection with steps  556  of  FIG.  5 B and  784    of  FIG.  7 B . Transitioning playback may also involve retrieving the audio content from an audio source and resuming playback of the particular audio content via the connected headphones, as illustrated by steps  557  and  558  of  FIG.  5 B  and steps  785  and  786  of  FIG.  7 B . 
     In another example, the playback device  102  may transition playback. For instance, the playback device  102  may stop playback of the retrieved audio content (e.g., by muting playback or stopping playback entirely). The playback device  102  may cause the control device  103  to play back the audio content via the connected headphones, perhaps by sending the audio content and timing information to the control device  103 , as illustrated in step  786  of  FIG.  5 B . 
     d. Detect Disconnection of Headphones 
     Referring again to  FIG.  10   , at block  1008 , implementation  1000  involves detecting disconnection of headphones. For instance, the control device  103  may detect disconnection of headphones from control device  103 , as discussed at  562  in  FIG.  5 C  and at  792  in  FIG.  7 C . As discussed above, detecting disconnection of headphones may involve detecting a change in the state of a state variable indicating headphone connection status. 
     In another example, detecting disconnection of headphones involves receiving a message indicating that headphones  104  have been disconnected from connected to the control device  103 . For instance, the playback device  102  may receive such a message from the control device  103  via a network interface. In some examples, the playback device  102  may receive such messages from multiple control devices  103  (e.g., from control device  103   a  and control device  103   b  as shown in  FIG.  7 D ). 
     e. Transition Playback From Headphones to Playback Device(s) 
     In  FIG.  10   , at block  1010 , implementation  1000  involves transitioning playback from headphones to one or more playback devices. For instance, the control device  103  may transition playback from the control device  103  via headphones  104  to the playback device(s)  102  based on detecting that the headphones are disconnected from the control device  103 . In another example, a given playback device  102  may transition playback from the control device  103  via headphones  104  to the playback device(s)  102  based on detecting that the headphones are connected to the control device  103   
     As noted above, the control device  103  may transition playback. Transitioning playback may involve to stopping playback of the particular audio content, as described in connection with step  793  of  FIG.  7 C . Transitioning playback may also involve causing the playback device(s)  102  to resume playback of the audio content, as illustrated by step  563  of  FIG.  5 C  and step  794  of  FIG.  7 C . 
     In another example, the playback device  102  may transition playback. For instance, the playback device  102  may cause the control device  103  to stop playback (e.g., by ceasing to provide the audio content and/or timing information to the control device  103 ). The playback device  102  may start playback by retrieving the audio content or unmuting playback, among other examples. 
     V. Conclusion 
     The description above discloses, among other things, various example systems, methods, apparatus, and articles of manufacture including, among other components, firmware and/or software executed on hardware. It is understood that such examples are merely illustrative and should not be considered as limiting. For example, it is contemplated that any or all of the firmware, hardware, and/or software aspects or components can be embodied exclusively in hardware, exclusively in software, exclusively in firmware, or in any combination of hardware, software, and/or firmware. Accordingly, the examples provided are not the only way(s) to implement such systems, methods, apparatus, and/or articles of manufacture. 
     (Feature 1) A method comprising while headphones are disconnected from the first control device, receiving, via a network interface of the first control device, an indication of particular audio content being played back by a first zone of the media playback system, wherein the first zone comprises one or more playback devices that are separate and distinct from the first control device and connected to the first control device via a local area network; while the particular audio content is being played back by the one or more playback devices of the media playback system, detecting that headphones have been connected to the first control device, wherein headphones are connectable to the first control device via either (a) an analog headphone jack of the first control device or (b) a point-to-point personal area network connection via a personal area network interface of the first control device; and in response to detecting that the headphones are connected to the first control device of the media playback system: (i) causing, via the network interface of the first control device, the one or more playback devices of the first zone to stop playback of the particular audio content; (ii) retrieving, via the network interface of the first control device, the particular audio content from an audio source that is remote from the first control device; and (iii) resuming playback of the particular audio content via the connected headphones. 
     (Feature 2) The method of feature 1, further comprising: while the first control device is playing back the particular audio content via the connected headphones, detecting that the headphones have been disconnected from the first control device; in response to detecting that the headphones have been disconnected from the first control device, (i) stopping playback of the particular audio content by the first control device and (ii) causing a graphical display to display a selectable control, that when selected, causes one or more playback devices of the first zone to resume playback of the particular audio content; and in response to detecting input data indicating a selection of the selectable control, that when selected, causes the one or more playback devices of the first zone to resume playback of the particular audio content, causing, via the network interface of the first control device, the one or more playback devices of the first zone to resume playback of the particular audio content. 
     (Feature 3) The method of feature 1, further comprising: while the first control device is playing back the particular audio content via the connected headphones, detecting that the headphones have been disconnected from the first control device; in response to detecting that the headphones have been disconnected from the first control device, (i) stopping playback of the particular audio content by the first control device and (ii) determining whether a policy of the first zone indicates that playback is resumed when headphones have been disconnected from the first control device; and in response to determining that the policy of the first zone indicates that playback is resumed when headphones have been disconnected from the first control device, causing, via the network interface of the first control device, the one or more playback devices of the first zone to resume playback of the particular audio content. 
     (Feature 4) The method of feature 3, wherein the policy indicates that playback is resumed when headphones have been disconnected from the first control device during a portion of a 24 hour cycle and the policy indicates that playback is not resumed when headphones have been disconnected from the first control device during the remainder of the 24 hour cycle. 
     (Feature 5) The method of feature 1, wherein detecting that headphones have been connected to the first control device comprises detecting that a state variable stored in data storage of the first control device has been modified to indicate that headphones are connected to the first control device, wherein the state variable is updated by at least one of (a) a circuit within the analog headphone jack of the first control device or (b) the personal area network interface of the first control device. 
     (Feature 6) The method of feature 1, wherein retrieving the particular audio content from the audio source that is remote from the first control device comprises: joining the first control device as a second zone into a zone group that includes the first zone; and receiving, via the network interface of the first control device from a zone group coordinator of the zone group, a data stream representing (i) the particular audio content for playback by the first control device via the headphones and (ii) playback timing information indicating a playback schedule for the first control device to play back the particular audio content via the connected headphones in synchrony with the one or more playback devices of the first zone, wherein the one or more playback devices are muted, and wherein the zone group coordinator is a given playback device of the first zone. 
     (Feature 7) The method of feature 1, wherein the first zone comprises a given playback device comprising a line-in interface, and wherein retrieving the particular audio content from the audio source that is remote from the first control device comprises receiving, via the network interface of the first control device from the given playback device, an audio stream representing the particular audio content received by the given playback device via the line-in interface. 
     (Feature 8) The method of feature 7, wherein the particular audio content is an audio track of video content, wherein the line-in interface of the given playback device is connected to a television, and wherein retrieving the particular audio content from the audio source that is remote from the first control device comprises receiving, via the network interface of the first control device from the given playback device, the audio stream representing the particular audio content for playback by the first control device via the connected headphones in sync with video content playing on the television. 
     (Feature 9) The method of feature 1, wherein the first zone comprises multiple playback devices, and wherein causing the one or more playback devices of the first zone to stop playback of the particular audio content comprises sending, via the network interface of the first control device to a group coordinator of the first zone, an instruction to cause the group coordinator of the first zone to stop synchronous playback of the particular audio content among the multiple playback devices of the first zone, wherein the group coordinator is a given playback device of the first zone that provides, to other playback devices of the first zone, a data stream representing (i) the particular audio content and (ii) playback timing information indicating a playback schedule for the multiple playback devices to play back the particular audio content in synchrony. 
     (Feature 10) The method of feature 1, wherein the first zone is in a zone group with a second zone that comprises one or more additional playback devices, and wherein causing the one or more playback devices of the first zone to stop playback of the particular audio content comprises sending, via the network interface of the first control device to the first zone and the second zone, respective instructions to stop synchronous playback of the particular audio content. 
     (Feature 11) A tangible, non-transitory computer-readable medium having stored therein instructions executable by one or more processors to cause a device to perform the method of any of features 1-10. 
     (Feature 12) A control device configured to perform the method of any of features 1-10. 
     (Feature 13) A system configured to perform the method of any of features 1-10. 
     (Feature 14) A method to be carried out by a playback device comprising an audio stage comprising an amplifier, one or more speakers, an I/O interface comprising a network interface, one or more processors, a housing carrying the audio stage, the one or more speakers, the network interface, the one or more processors and data storage having stored therein instructions executable by the one or more processors to cause the playback device to perform the method, the methods comprising: receiving, via the network interface from a first control device of the media playback system, an instruction to play back audio content, wherein the first control device is separate and distinct from the playback device; in response to receiving the instruction to play back audio content, (i) retrieving, via the I/O interface, the audio content from an audio source that is remote from the playback device and (ii) playing back the retrieved audio content via the audio stage and the one or more speakers; while playing back the retrieved audio content via the audio stage and the one or more speakers, receiving, via the network interface from the first control device, a message indicating that first headphones are connected to the first control device of the media playback system; and in response to receiving the message indicating that the first headphones are connected to the first control device of the media playback system: (i) stopping playback of the retrieved audio content via the audio stage and the one or more speakers and (ii) causing, via the network interface, the first control device to play back the audio content via the first headphones. 
     (Feature 15) The method of feature 14, further comprising: while the first control device is playing back the audio content via the first headphones, receiving, via the network interface from the first control device of the media playback system, a message indicating that that the first headphones are disconnected from the first control device of the media playback system; and in response to receiving the message indicating that the first headphones are disconnected from the first control device of the media playback system, starting playback of the retrieved audio content at a muted volume level via the audio stage and the one or more speakers at a play position corresponding to when the first headphones were disconnected from the first control device of the media playback system. 
     (Feature 16) The method of feature 14, further comprising: while the first control device is playing back the audio content via the first headphones, receiving, via the network interface from a second control device of the media playback system, a message indicating that second headphones are connected to the second control device of the media playback system, wherein the second control device is separate and distinct from the playback device and the first control device; and in response to receiving the message indicating that the second headphones are connected to the second control device of the media playback system, causing, via the network interface, the second control device to play back the audio content via the second headphones in synchrony with the first control device via the first headphones. 
     (Feature 17) The method of feature 16, further comprising: while the first control device and the second control device are playing back the audio content via the first headphones and the second headphones, respectively, receiving, via the network interface from the first control device of the media playback system, a message indicating that that the first headphones are disconnected from the first control device of the media playback system; and in response to receiving the message indicating that the first headphones are disconnected from the first control device of the media playback system, causing, via the network interface, the second control device to stop playing back the audio content via the second headphones. 
     (Feature 18) The method of feature 16, wherein causing the second control device to play back the audio content via the second headphones in synchrony with the first control device via the first headphones comprises: transmitting, via the network interface to the first control device, (i) the audio content for playback by the first control device via the first headphones and (ii) playback timing information indicating a playback schedule for the first control device to play back the audio content via the first headphones in synchrony with the second control device; and transmitting, via the network interface to the second control device, (i) the audio content for playback by the first control device via the first headphones and (ii) playback timing information indicating a playback schedule for the second control device to play back the audio content via the second headphones in synchrony with the first control device. 
     (Feature 19) The method of feature 14, wherein the I/O interface comprises a line-in interface, wherein retrieving, via the I/O interface, the audio content from an audio source that is remote from the playback device comprises receiving the audio content from via the line-in interface, and wherein causing, via the network interface, the first control device to play back the audio content via the first headphones comprises streaming, via the network interface, the audio content to the first control device for playback by the first control device via the first headphones. 
     (Feature 20) The method of feature 19, wherein the audio content is an audio track of video content, wherein the line-in interface is connected to a television, and wherein causing, via the network interface, the first control device to play back the audio content via the first headphones comprises streaming, via the network interface, the audio content to the first control device for playback by the first control device via the first headphones in sync with video content playing on the television. 
     (Feature 21) The method of feature 19, wherein streaming the audio content to the first control device for playback by the first control device via the first headphones comprises hosting the audio content in data storage of the playback device, and wherein causing, via the network interface, the first control device to play back the audio content via the first headphones comprises sending, via the network interface to the first control device, a uniform resource identifiers indicating a locations of the audio content at the playback device. 
     (Feature 22) The method of feature 14, wherein the audio content comprises one or more audio tracks of a streaming audio service, and wherein causing, via the network interface, the first control device to play back the audio content via the first headphones comprises sending, via the network interface to the first control device, one or more uniform resource identifiers indicating respective locations of the one or more audio tracks at one or more servers of a streaming audio service. 
     (Feature 23) The method of feature 14, wherein stopping playback of the retrieved audio content via the audio stage and the one or more speakers comprises muting playback of the retrieved audio content via the audio stage and the one or more speakers. 
     (Feature 24) A tangible, non-transitory computer-readable medium having stored therein instructions executable by one or more processors to cause a device to perform the method of any of features 14-23. 
     (Feature 25) A playback device configured to perform the method of any of features 14-23. 
     (Feature 26) A system configured to perform the method of any of features 14-23. 
     The specification is presented largely in terms of illustrative environments, systems, procedures, steps, logic blocks, processing, and other symbolic representations that directly or indirectly resemble the operations of data processing devices coupled to networks. These process descriptions and representations are typically used by those skilled in the art to most effectively convey the substance of their work to others skilled in the art. Numerous specific details are set forth to provide a thorough understanding of the present disclosure. However, it is understood to those skilled in the art that certain embodiments of the present disclosure can be practiced without certain, specific details. In other instances, well known methods, procedures, components, and circuitry have not been described in detail to avoid unnecessarily obscuring aspects of the embodiments. Accordingly, the scope of the present disclosure is defined by the appended claims rather than the forgoing description of embodiments. 
     When any of the appended claims are read to cover a purely software and/or firmware implementation, at least one of the elements in at least one example is hereby expressly defined to include a tangible, non-transitory medium such as a memory, DVD, CD, Blu-ray, and so on, storing the software and/or firmware.