W3C home > Mailing lists > Public > public-html-a11y@w3.org > February 2010

Re: [media] Moving forward with captions / subtitles

From: Philip Jägenstedt <philipj@opera.com>
Date: Fri, 19 Feb 2010 15:00:31 +0800
To: "Eric Carlson" <eric.carlson@apple.com>
Cc: "Silvia Pfeiffer" <silviapfeiffer1@gmail.com>, "Geoff Freed" <geoff_freed@wgbh.org>, "HTML Accessibility Task Force" <public-html-a11y@w3.org>
Message-ID: <op.u8c4e5l4atwj1d@philip-pc>
On Fri, 19 Feb 2010 13:43:19 +0800, Eric Carlson <eric.carlson@apple.com>  

> On Feb 17, 2010, at 9:49 PM, philipj@opera.com wrote:
>> On Thu, 18 Feb 2010 00:31:17 +0800, Eric Carlson  
>> <eric.carlson@apple.com>
>>>  Some questions and thoughts, in no particular order:
>>> +  I assume that if I use our track API to examine the track tracks in  
>>> a trackgroup, the one chosen from among a group of alternates is  
>>> enabled, and the others are not?
>> What does enabled mean here? Since the MediaTracks API doesn't reflects
>> the concept of groups, the mapping is open for debate. I think we should
>> either reflect groups in some way, or we should simply expose all tracks
>> in all groups (enabled or not) and setting .enabled=true on a track  
>> should
>> implicitly disable the others in the same group.
>   We should definitely expose all tracks, whether or not they are in a  
> group. We could expose group, but what could a script do with it?

It would be good if a script can tell if enabling a track will disable  
others, so that it doesn't walk through the list and try to enable all  
tracks and is then surprised by the results. There is a workaround for  
<trackgroup><track> (look at the DOM tree), but what about embedded tracks?

>>> + Do we enable the first track in a group if none match?
>> I don't think so, but we haven't discussed the track selection algorithm
>> much at all. I suppose it should first find the the first track with the
>> enabled="" attribute in each group and enable that. But do we also want  
>> an
>> enabled attribute on the group itself that performs selection based on
>> media type, language, role etc?
> The whole point of <trackgroup> is to mark some number of tracks that  
> are alternates of one another, so the *user agent* can choose which one  
> is most appropriate to enable based on conditions on the user's machine  
> (user preferences, machine characteristics, etc). If we are just going  
> to allow the user to specify which one is enabled, why bother with the  
> grouping at all?

It would be useful even without a track selection algorithm as it would  
allow the UA and scripts to create appropriate menus and the UA can  
guarantee that at most 1 track in the same group is enabled.

Still, I agree that we should have a track selection algorithm that takes  
at least media into account like for <source> resource selection. I'll  
note that I'm less than optimistic about automatic language selection  
being useful, because UA language is too often set to something  

Philip Jägenstedt
Core Developer
Opera Software
Received on Friday, 19 February 2010 07:01:27 UTC

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