Re: [media] a first draft JavaScript API for multitrack media

On Wed, Feb 17, 2010 at 4:37 PM, Philip Jägenstedt <philipj@opera.com> wrote:
> On Wed, 17 Feb 2010 11:44:32 +0800, Silvia Pfeiffer
> <silviapfeiffer1@gmail.com> wrote:
>
>> Hi all, and in particular media subgroup,
>>
>> Today we had a phone discussion about the JavaScript API spec and we
>> realised that we haven't actually specified the list of roles that the
>> @roles attribute should accept.
>>
>> So, I wanted to start a discussion on this with the goal of eventually
>> reaching a list that we can all agree on to cover the known use cases.
>>
>> Let me start by stating that in today's call everyone agreed that we
>> need to come up with a determined list of values for the roles, so if
>> you disagree with that, you should speak up now.
>
> In all discussions so far role is only an attribute that exists in the
> markup without having any influence on... well anything. I would like to see
> suggestions on how UAs should use roles (e.g. in a track selection
> algorithm) before investing effort in defining them.

There are three particular use cases for UAs of roles:

Firstly, they put all the tracks together in the same css styling
class, so that you can e.g. switch between subtitles and they are
still presented in the same way. Tracks with different roles should
not have the same styling. Of course, this can be overruled by the
page author, but this applies to the defaults.

Secondly, they provide a means of grouping things together that are
tightly related and most of the time presented as alternatives (even
if the media resource had not marked these tracks as alternatives).

Thirdly, they provide a semantic hint for applications/UAs as to what
is in the track. So, if your browser preference says "always
automatically activate all subtitles in Swedish" then you can find the
subtitle track in Swedish.

I thought this was obvious, but it's good to actually state it all. :-)

Cheers,
Silvia.

Received on Wednesday, 17 February 2010 06:26:38 UTC