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

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

--- Comment #2 from Cyril Concolato <cyril.concolato@telecom-paristech.fr> ---
(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.

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

[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."

-- 
You are receiving this mail because:
You are the QA Contact for the bug.

Received on Wednesday, 8 October 2014 19:37:18 UTC