Inband tracks: NGA audio preselections

[poolec]

At least two of the WAVE audio media profiles (ca4s and cmhs) carry audio data that can describe multiple preselections (e.g. with different languages, clean audio options, audio description etc.).

It would be desirable for an application to be able to choose from these since without that capability, a significant feature of these codecs is not accessible.

The most straightforward way for this feature to be supported for HTML5 video would be if each preselection gave rise to a separate AudioTrack, with appropriate track metadata. To enable that, it would fall to an inband tracks specification to specify the mapping. So, logically, the CMAF inband tracks mapping should consider NGA audio codecs and provide a mapping from preselections to AudioTracks.

This might be too big an issue to resolve in a first version of the CMAF inband tracks spec and may depend on spec changes elsewhere to make it straightforward to implement and general enough to work with all relevant audio codecs, but I wanted to raise the issue now and see what other interest there is in pursuing this.

[haudiobe]

Call 2020/11/19: Not easily fixed, but important topic. Should be brought to attention of MPEG CMAF and W3C. However, we do not expect to solve this in short time, so we leave this for discussion.