W3C home > Mailing lists > Public > public-html-media@w3.org > September 2012

[MSE] Questions about setting track language & kind (Bug 17006)

From: Aaron Colwell <acolwell@google.com>
Date: Fri, 21 Sep 2012 11:09:45 -0700
Message-ID: <CAA0c1bAhYB=HPHgGBqw4PwwQLTiHBTc5bTpDp=Wm3zH=3iGLyg@mail.gmail.com>
To: "<public-html-media@w3.org>" <public-html-media@w3.org>
Hi,

On one of the calls several weeks ago I said I'd start a thread about
several questions I had about Bug
17006<https://www.w3.org/Bugs/Public/show_bug.cgi?id=17006>.
Here it is. :) The goal of this bug is to provide a way to reflect the role
& language specified in a DASH manifest in the {Audio | Video | Text}Track
objects.

I've spent some time trying to understand the DASH spec and have come up
with these questions:

1. Do people still want this feature? I believe it was one of the open
issues our friends at Microsoft asked to be included in the original
proposal.

2. Why would it be better to put this information in the manifest instead
of the initialization segments? Don't they have role & language information
encoded in them?

3. It looks like language & role can be specified at the AdaptationSet &
ContentComponent level. How should these be treated differently in the
Media Source context?

4. In the context of this bug, are we assuming a 1:1 mapping between
AdaptationSets and SourceBuffers? (ie Representations from different
AdaptationSets won't be mixed)

5. Are contentComponent id's specified in SubRepresentations  required to
have the same language and role across all Representations in an
AdaptationSet? If not, I believe this could mean the language for tracks
could change if the application switches representations in an adaptation
set.

6. There don't appear to be trackIDs mentioned in the manifest. Is it safe
to assume that role & language apply to all tracks within the
representation? If so, how are alternate language tracks represented within
an AdaptationSet?

7. What is the expected behavior if the language of a track suddenly
changes? Say I have 2 audio tracks. Track 1 is English and track 2 is
French. My preferred language is English so track 1 is selected. I then
append a new initialization segment that indicates track 1 has French and
track 2 is English along with a few media segments.
  a. Should the UA switch to track 2 at the appropriate time so that
English audio is always output?
  b. Should this kind of language change be rejected?


Aaron
Received on Friday, 21 September 2012 18:10:16 GMT

This archive was generated by hypermail 2.2.0+W3C-0.50 : Friday, 21 September 2012 18:10:17 GMT