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Re: Spec question - multiple video tracks in a MediaStream?

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Thu, 25 Aug 2011 13:29:40 +0200
Message-ID: <4E563224.5050406@ericsson.com>
To: public-webrtc@w3.org
On 2011-08-25 13:16, Harald Alvestrand wrote:
> On 08/25/11 12:44, Stefan Håkansson LK wrote:
>> On 2011-08-25 11:34, Harald Alvestrand wrote:
>>> This came up on my team while implementing, and I'm posting it so we do
>>> not forget:
>>>
>>> If there are multiple video tracks active in a MediaStream, how should
>>> we connect them to<video> tags?
>>>
>>> At the moment, the connection goes via URLs, and the URL is a function
>>> of the MediaStream, not of a track in the MediaStream. And I don't think
>>> <video> has a defined behaviour for playing multiple video tracks at
>>> once.
>>>
>>> Possible solutions:
>>>
>>> - Declare that there can be at most one video track active in a
>>> MediaStream (this was true at one point)
>>> - Give the URL-generating function an optional parameter for the track
>>> index (defaulting to first video)
>>> - Feed the URL-generating function a track instead of a MediaStream
>>> - Just leave this behaviour undefined?
>> One solution is outlined in step 9 of
>> <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#getting-media-metadata>
>> (selects the first active video track for rendering).
> This text is:
>
>  1.
>
>     If either themedia resource
>     <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#media-resource>or
>     the address of thecurrent media resourceindicate a particular set of
>     audio or video tracks to enable, then the selected audio tracks must
>     be enabled in the element's|audioTracks
>     <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#dom-media-audiotracks>|object,
>     and, of the selected video tracks, the one that is listed first in
>     the element's|videoTracks
>     <http://www.whatwg.org/specs/web-apps/current-work/multipage/the-video-element.html#dom-media-videotracks>|object
>     must be selected
>
> I don't have a problem with that; if we have 2 video tracks and need to
> show them both, we can duplicate the MediaStream and disable the 1st
> track in the copy, then feed them to different <video> tags.
I'm also fine with this solution.

Also, just to be clear, the text same in the w3c version of the html 
spec 
(<http://dev.w3.org/html5/spec/Overview.html#loading-the-media-resource>).
>
> The behaviour of <video> is something we don't want to specify in our
> document if we can avoid it, I think.
Received on Thursday, 25 August 2011 11:30:14 GMT

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