Select playback of certain audio track(s) associated with a video

[zimeon]

Description

A user should be able to select which audio track or tracks they would like to hear from a video resource. How would information to allow selection be conveyed through the Presentation API description of the resource? Client side implementation of features like #30.

Variation(s)

...

Proposed Solutions

Additional information in Presentation API

Additional Background

Created after discussion of #30 at 2017-02 AV workshop

[bvibber]

For HTML5 video, per spec you can query the audio track list and set the active track, but browsers may or may not actually handle it; IIRC Firefox specifically supports only the first audio track it finds in a particular file.

MPEG-DASH and HLS often separate the audio and video tracks to separate files, allowing the DASH player to change tracks by changing which subset of chunk files it loads into the decoder. Not sure offhand if HLS in native Safari playback exposes audio track switching to JS.

For referencing the tracks: media fragment spec has a 'track' option but its terminology is not very well defined. Only ?track=audio and ?track=video are given as actual example values -- see https://www.w3.org/TR/media-frags/ and https://www.w3.org/TR/2011/WD-media-frags-recipes-20111201/ -- but it's unclear how one would specify anything more complex like "the Dutch subtitle track" or "the English closed-caption track"