Audio caching for synchronous playback

Tangible, non-transitory computer readable media comprising program instructions stored therein, wherein the program instructions, when executed by one or more processors, cause a first playback device to perform functions comprising:

• maintaining a cache at the first playback device comprising a plurality of audio tracks, wherein an individual audio track comprises a series of frames, and wherein an individual frame comprises a portion of the individual audio track;
• after receiving a request to play a particular audio track, determining whether the particular audio track is stored in the cache at the first playback device;
• when the particular audio track is stored in the cache at the first playback device, (i) identifying playback timing for each frame of the series of frames stored in the cache at the first playback device based at least in part on a current clock time of a clock at the first playback device, and (ii) playing individual frames in the series of frames comprising the portions of the particular audio track according to the playback timing for the individual frames;
• when the particular audio track is not stored in the cache at the first playback device, obtaining the particular audio track from an audio information source;
• wherein when the first playback device is configured as a group coordinator for a playback group comprising the first playback device and a second playback device, and wherein identifying playback timing for each frame of the series of frames stored in the cache at the first playback device based at least in part on the current clock time of the clock at the first playback device comprises:
• for an individual frame, configuring a playback time that is indicative of a future time relative to the current clock time of the clock at the first playback device;
• wherein when the particular audio track is stored in the cache at the first playback device, the functions further comprise:
• determining whether the particular audio track is stored in a cache at the second playback device;
• when the particular audio track is stored in the cache at the second playback device, transmitting the playback timing for the particular audio track to the second playback device;
• and
• when the particular audio track is not stored in the cache at the second playback device, transmitting the series of frames comprising the portions of the particular audio track and the corresponding playback timing from the first playback device to the second playback device.

A method performed by a first playback device, wherein the method comprises:

• maintaining a cache at the first playback device, wherein the cache comprises a plurality of audio tracks, wherein an individual audio track comprises a series of frames, and wherein an individual frame comprises a portion of the individual audio track;
• after receiving a request to play a particular audio track, determining whether the particular audio track is stored in the cache at the first playback device;
• when the particular audio track is stored in the cache at the first playback device, (i) identifying playback timing for each frame of the series of frames stored in the cache at the first playback device based at least in part on a current clock time of a clock at the first playback device, and (ii) playing individual frames in the series of frames comprising the portions of the particular audio track according to the playback timing for the individual frames;
• when the particular audio track is not stored in the cache at the first playback device, obtaining the particular audio track from an audio information source;
• wherein when the first playback device is configured as a group coordinator for a playback group comprising the first playback device and a second playback device, and wherein identifying playback timing for each frame of the series of frames stored in the cache at the first playback device based at least in part on the current clock time of the clock at the first playback device comprises:
• for an individual frame, configuring a playback time that is indicative of a future time relative to the current clock time of the clock at the first playback device;
• wherein when the particular audio track is stored in the cache at the first playback device, the functions further comprise:
• determining whether the particular audio track is stored in a cache at the second playback device;
• when the particular audio track is stored in the cache at the second playback device, transmitting the playback timing for the particular audio track to the second playback device;
• and
• when the particular audio track is not stored in the cache at the second playback device, transmitting the series of frames comprising the portions of the particular audio track and the corresponding playback timing from the first playback device to the second playback device.