Re: [media] Moving forward with captions / subtitles

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?

>> + I also assume that if I set the enabled property on one track in a group all of the others are automatically disabled?
> 
> Yes.
> 
>> + 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?

In other words, it is the job of the content author to describe each tracks in a group so the UA can pick the best one for the user. If the content author wants to choose which one is enable, they should not use a <trackgroup>.

eric