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Re: [media] Moving forward with captions / subtitles

From: Silvia Pfeiffer <silviapfeiffer1@gmail.com>
Date: Tue, 16 Feb 2010 23:11:50 +1100
Message-ID: <2c0e02831002160411n84c43ccy4234c1b0f4ace82e@mail.gmail.com>
To: Philip Jägenstedt <philipj@opera.com>
Cc: Geoff Freed <geoff_freed@wgbh.org>, Eric Carlson <eric.carlson@apple.com>, HTML Accessibility Task Force <public-html-a11y@w3.org>
On Tue, Feb 16, 2010 at 7:19 PM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Tue, 16 Feb 2010 15:46:00 +0800, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
>
>> On Tue, Feb 16, 2010 at 6:37 PM, Philip Jägenstedt <philipj@opera.com>
>> wrote:
>>>
>>> On Tue, 16 Feb 2010 04:36:09 +0800, Geoff Freed <geoff_freed@wgbh.org>
>>> wrote:
>>>
>>>> GF:  I prefer <trackgroup><track> as well--  grouping tracks by role
>>>> makes
>>>> the most sense to me. But I'm still confused about one thing after
>>>> reading
>>>> today's thread.  From this markup, it looks to me like
>>>> <trackgroup><track>
>>>> also would permit multiple tracks of the same role to appear
>>>> simultaneously.
>>>>  True?  Playing simultaneous tracks of the same role is still what I'd
>>>> prefer (in addition to playing simultaneous tracks of differing roles,
>>>> of
>>>> course).
>>>
>>> My idea is that <trackgroup> be used to group mutually exclusive tracks,
>>> independently of their roles. I struggle to come up with an example when
>>> you
>>> would want it, but if you wrap each <track> in its own <trackgroup> then
>>> *all* tracks can be enabled simultaneously. It is of course up to the
>>> author
>>> to make groups that make sense. Power users could override this using
>>> user
>>> JavaScript or other browser extensions if they really want to.
>>
>> I'd actually prefer the opposite functionality - and that would also
>> be much more like what is in a media resource:
>>
>> <track>s in a list without <trackgroup> can be activated in parallel -
>> they are like non-grouped MP4 tracks.
>>
>> <track>s inside a <trackgroup> are mutually exclusive - only one of
>> them can be activated at any point in time.
>>
>> IIUC, that's how grouping works in MP4 and QuickTime and thus applying
>> this same principle here seems to make sense to me. Thus, if you
>> didn't want tracks to be active together, you'd pack them in a
>> trackgroup. Much easier than having to package each single <track> in
>> a <trackgroup> to enable them to be active in parallel.
>
> If I understand you, the only difference is the semantics when <trackgroup>
> is omitted. We can make either behavior the default. What it comes down to
> is what authors actually expect and which case is more common. I don't know
> anything about MPEG-4, but I do know that for any file with multiple text
> tracks I have opened in any media player (software or hardware), tracks have
> been mutually exclusive.

That's probably because the only text tracks that have been regarded
so far were captions and subtitles. It's easy to only deal with such
as mutually exclusive. I think we have new opportunities here for the
Web. We have, for example, the possibility to bring in textual audio
descriptions that can hook up with screenreaders - something that has
not been done before (or at least not in a big scale).

I actually believe that in future we may see a lot more files that
have both, mutually exclusive tracks and additional tracks. Things
such as:

<video src="video.ogv">
       <track src="cc.en.srt" srclang="en" role="CC" active>
       <track src="tad.en.srt" srclang="en" role="TAD">
       <track role="SUB">
           <source src="subs.de.srt" srclang="de">
           <source src="subs.sv.srt" srclang="sv">
           <source src="subs.jp.srt" srclang="jp">
       </track>
 </video>

In this case, the CC, the TAD and and one of the SUBs can (but don't
have to) be active in parallel.

> (Also, I don't want to come up with a UI for enabling multiple tracks when
> there is no grouping, as it would have to be something strange like a list
> of checkboxes in a context menu.)

The UI for this would be:

CC -> en
TAD -> en
SUB
      -> de
      -> sv
      -> jp

This is a bit inspired by the menu of YouTube, but extended with all
the other text tracks.

Cheers,
Silvia.
Received on Tuesday, 16 February 2010 12:12:43 GMT

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