Alternate audio tracks in the playlist

The playlist for a video can specify an unlimited number of alternative audio tracks for the main video content. With the PSDK, you can use these alternative tracks. For example, you might want to add different languages to your video content or allow the user to switch between different tracks on their device while the content is playing. This is known as late-binding audio.

Late-binding audio is the support of multiple language tracks for HTTP video streams (live/linear and VOD) without having to modify, duplicate, or repackage the video for each audio track. Late binding of an audio track allows you to easily provide multiple language tracks for a video asset at any time before or after the asset’s initial packaging.

In order for the alternate audio to be mixed with the video track of the main media, the timestamps of the alternate track must match the timestamps of the audio in the main track.

The following requirements apply if you use alternate audio tracks and incorporate advertising:

If the main content has alternate audio tracks, ads must at least have an audio-only stream.
Each segment duration of an ad's audio-only stream must be equal to the segment duration of an ad's video stream.

The main audio track is included in the audio tracks collection with the label “default”. Metadata for the alternate audio streams is included in the playlist in the #EXT-X-MEDIA tags with TYPE=AUDIO.

For example, an M3U8 manifest that specifies multiple alternate audio streams might look like this:

#EXTM3U
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="bipbop_audio",LANGUAGE="eng",NAME="BipBop Audio 1",
 AUTOSELECT=YES,DEFAULT=YES
#EXT-X-MEDIA:TYPE=AUDIO,GROUP-ID="bipbop_audio",LANGUAGE="eng",NAME="BipBop Audio 2",
 AUTOSELECT=NO,DEFAULT=NO,URI="alternate_audio_aac/prog_index.m3u8"
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="English",AUTOSELECT=YES,FORCED=NO,
 LANGUAGE="eng",URI="subtitles/eng/prog_index.m3u8"
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="English (Forced)",DEFAULT=YES,
 AUTOSELECT=YES,FORCED=YES,LANGUAGE="eng",URI="subtitles/eng_forced/prog_index.m3u8"
#EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="subs",NAME="Français",AUTOSELECT=YES,FORCED=NO,
 LANGUAGE="fra",URI="subtitles/fra/prog_index.m3u8"
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=263851,CODECS="mp4a.40.2, avc1.4d400d",
 RESOLUTION=416x234,AUDIO="bipbop_audio",SUBTITLES="subs" 
gear1/prog_index.m3u8
#EXT-X-STREAM-INF:PROGRAM-ID=1,BANDWIDTH=577610,CODECS="mp4a.40.2, avc1.4d401e",
 RESOLUTION=640x360,AUDIO="bipbop_audio",SUBTITLES="subs"
gear2/prog_index.m3u8
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