Proposal for initial CG focus

Hi,

I'd like to start the discussion about the requirements and scope for the
CG work.

Currently, AFAIK there is no specification that fully defines how a UA
should expose in-band tracks to Web applications.  Unspecified details are:

* Which in-band tracks of a media resource the UA will expose.By expose I
mean make available as VideoTrack, AudioTrack or TextTrack objects.
* How metadata in the media resource about the in-band tracks is made
available to Web applications. If the UA recognizes the in-band track,
some of the metadata associated with the track will be made available by
the "kind", "language" and "inbandMetadataTrackDispatchType"  attributes.
This works fine when the UA fully recognizes the track and when the
metadata maps completely to the predefined valid attribute values. But,
this needn't be the case. For example, the UA may recognize an MPEG-2 TS
audio track but not recognize metadata designating it as a Descriptive
Video track.

For more deterministic handling of inband tracks, the UA could be required
to:

* Expose all in-band tracks, in some form.
* Make media resource metadata  associated with the inband tracks
available to Web applications. [1] does this through a TextTrack.
* Provide data so that the Web application can correlate the metadata data
with the appropriate Track object.

[1] is a specification written by CableLabs about how a UA would meet
these requirements in the case of MPEG-2 transport stream media resources.
This spec was written before some of the recent additions to HTML5, e.g.
inbandTrackDispatchType. The users of [1] would like to see a W3C spec
that addresses the same problem, takes into account the current HTML5.1
work and addresses some details that [1] missed, e.g. more precise
definition of what constitutes a metadata TextTrack, how in-band data gets
segmented into TextTrackCues, how Cue start and end times are derived from
the in-band track.

[2] is an informal draft describing how the technique in [1] can be
applied to WebM, Ogg and MPEG4 media resources. This CG could address
these media container formats as well.

So, at a minimum, I propose:

* That the CG start by discussing the requirements outlined above, with
the goal of creating a spec at least for MPEG-2 TS (recognizing that some
of this may already be covered by HTML5/1.
* WebM and MP4 are widely supported in browsers so it might make sense to
cover these formats.

If there is sufficient interest, we could take on other inband track
formats as well.

Comments?

[1] http://www.cablelabs.com/specifications/CL-SP-HTML5-MAP-I02-120510.pdf
[2] http://html5.cablelabs.com/tracks/media-container-mapping.html

Thanks,
Bob

Received on Thursday, 31 October 2013 20:10:30 UTC