[Bug 26923] [InbandTracks] Number of HTML tracks from DASH

https://www.w3.org/Bugs/Public/show_bug.cgi?id=26923

--- Comment #3 from Bob Lund <b.lund@cablelabs.com> ---
(In reply to Cyril Concolato from comment #2)
> (In reply to Bob Lund from comment #1)
> > (In reply to Cyril Concolato from comment #0)
> > > "A user agent recognises and supports data from a MPEG DASH media resource
> > > as being equivalent to a HTML track based on the AdaptationSet or
> > > ContentComponent mimeType:"
> > > It is unclear how many tracks should be created: 1 per AS or 1 per
> > > Representation, or 1 per ContentComponent.
> > 
> > This same question came up in Bug 26921 [1]. I commented that an HTML track
> > should be created for every AdaptationSet or child ContentComponent. I will
> > create a PR to clarify that.
> Let's have that discussion on that bug.

OK. Then this bug should be closed and marked as a duplicate of bug 26921.

> 
> > > Also, it is not clear which AS
> > > should be exposed ? All including those for which the mime type is not
> > > supported?

This question did not get addressed. It seems to make sense that the UA should
only create audio, video and non-metadata text tracks for media streams it can
render.

> > 
> > Good question. For DASH content played using MSE in HTML, if the UA doesn't
> > support the MIME type of an AS then it wouldn't be able to process
> > initialization segments and no tracks will be created for that resource. It
> > might be worth stating that this should be the case.
> Why do you suppose that the tracks will only be created using MSE? With
> video.addTextTrack() [2] you can create the track for types not supported by
> MSE. That's what I do in MP4Box.js [3]
> 

This bug was about creating tracks from the DASH MPD. Script created tracks is
another topic.

> [2]
> http://www.w3.org/html/wg/drafts/html/master/embedded-content.html#dom-media-
> addtexttrack 
> [3] https://github.com/gpac/mp4box.js
> 
> >  
> > > 
> > > Please rephrase using normative statements such as:
> > > "User agents shall expose HTML tracks for all AdaptationSet elements in an
> > > MPD. For  AdaptationSets for which the MIME type is not supported, it shall
> > > expose the associated tracks as HTML TextTracks. For AdaptationSets for
> > > which the MIME Type is supported, it shall expose AdaptationSet whose MIME
> > > main type is "video" (resp. "audio") as HTML VideoTracks (resp. AudioTracks)
> > > and as TextTracks for all others. In a given AdaptationSet, UA shall expose
> > > all Representations as an HTML Track. If representations carry multiplexed
> > > streams, the UA shall expose each ContentComponent as an HTML Track."
> > 
> > The Sourcing spec is informative, which is why the statements are not
> > normative.
> Why? Informative specs are not really useful. It should be normative. UA
> don't have to implement it, but if they decide to implement it, it should be
> done in a normative way. The MSE follows that approach for instance, it says:
> "If an implementation claims to support a MIME type listed in the registry,
> its SourceBuffer implementation must conform to the byte stream format
> specification listed in the registry entry."

Feel free to go down that path.

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Received on Wednesday, 8 October 2014 20:59:10 UTC