W3C home > Mailing lists > Public > public-html-media@w3.org > May 2014

Re: [MSE] Resolving Bug 24370

From: Aaron Colwell <acolwell@google.com>
Date: Mon, 12 May 2014 06:01:50 -0700
Message-ID: <CAA0c1bBc0Cp+4MZn-B6T_0cgxNOoN=Wdn8wiafW9csbmFO6aQQ@mail.gmail.com>
To: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Cc: Jim Ley <jim.ley@gmail.com>, "<public-html-media@w3.org>" <public-html-media@w3.org>
On Sun, May 11, 2014 at 12:37 PM, Silvia Pfeiffer <silviapfeiffer1@gmail.com
> wrote:

> On Thu, Apr 3, 2014 at 5:30 AM, Aaron Colwell <acolwell@google.com> wrote:
> >
> >
> > On Wed, Apr 2, 2014 at 6:20 AM, Jim Ley <jim.ley@gmail.com> wrote:
> >>
> >> On 2 April 2014 09:26, Silvia Pfeiffer <silviapfeiffer1@gmail.com>
> wrote:
> >>>
> >>> On Wed, Apr 2, 2014 at 6:04 PM, Jim Ley <jim.ley@gmail.com> wrote:
> >>> >
> >>> > Isn't the use case for language being mutable simply live subtitles
> of
> >>> > a
> >>> > live "channel" that has programmes in different languages and
> therefore
> >>> > has
> >>> > closed captions / subtitles in different languages.
> >>>
> >>> Each one of those subtitle languages would be a different track, so
> >>> there is no need for mutability.
> >>
> >>
> >> No they're not, some shows are in English, some are in Welsh, the
> subtitle
> >> track is a single one for the live broadcast, similarly with audio, the
> >> broadcast audio changes languages.
> >
> >
> > I think there are 2 separate issues here.
> > 1. How are language changes within an inband track supposed to be
> > represented in HTML5?
> Do you think we should mention language changes as another example
> where multiple tracks are created in
> http://rawgit.com/silviapfeiffer/HTMLSourcingInbandTracks/master/index.html
> ? Would that help clarify?

I was viewing that document as providing container specific mappings to
HTML5 concepts. It seems to me that if HTML5 expects xxxTrack objects to be
removed and readded when language and kind changes, then I feel like that
should be in the HTML5 spec. At a minimum I think it needs to provide
clarity about when and under what conditions xxxTrack objects are expected
to come and go throughout the life of the presentation. I don't think this
is clear especially for presentations where there are language changes or
the addition and removal of tracks in the middle of the presentation like a
SAP track coming and going whenever there is a change between a program and
a commercial. It also isn't clear to me whether seeking should cause
certain tracks to disappear/reappear if they aren't available in that
portion of the timeline. I don't feel like either of these things are
specified very well in the current HTML5 spec text.

On a related note, I think that the HTML5 spec should also mention that
multiple xxxTrack objects should be created if a track in the underlying
container has multiple kinds or languages associated with it. It was not
obvious to me that this was the intended behavior for this situation and I
think it deserves a sentence or 2 in the HTML5 spec. I think the HTML5 spec
text implies there is a 1-1 mapping between xxxTracks objects and tracks in
the container formats, but the discussions around language/kind changes,
multiple kinds, and things like VBI captions in a container level video
track make me believe that this is actually not true. All of these
situations result in multiple HTML5 tracks, according to my current
understanding, but only actually constitute a single track at the container
level. I'm not aware of any place in the HTML5 spec that these nuances are

Received on Monday, 12 May 2014 13:02:18 UTC

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