Re: Which videoTrack should be played in the <Video> element?

On 07/27/2012 02:47 PM, Travis Leithead wrote:
>
> The spec currently does not specify which videoTrack should be 
> displayed in the <Video> element when the video element is consuming a 
> MediaStream. When there is only one MediaStreamTrack in the videoTrack 
> list, this is obvious. But it is somewhat less obvious what should 
> happen when there are either:
>
> 1)No videoTracks (e.g., the user requested or received a MediaStream 
> with only audioTracks present)
>
> 2)More than one videoTracks that are enabled (enabled-by-default as 
> the spec says)
>
> May I suggest that the spec needs to address these two cases:
>
> 1.How should the video element consumer handle audio-only MediaStreams?
>
> 2.How should multiple videoTrack's be addressed when consumed by a 
> video element?
>
> For the multiple-video tracks case, the HTML5 video element handles 
> this by toggling the tracks in its videoTracks list 
> (http://dev.w3.org/html5/spec/single-page.html#videotracklist) such 
> that only one video track is active at a time; it has the concept of a 
> "selected" track and a "selectedIndex".
>
> My proposal for MediaStreams is that audio-only MediaStreams (being 
> consumed by a Video element) should result in a zero-sized media 
> dimension, and we should be sure to note in the spec that the media 
> element's videoWidth/videoHeight attributes are set to zero. For 
> MediaStreams with multiple videoTracks, I suggest that we either adopt 
> to model used by HTML5, or make the order of the Tracks significant, 
> such that when there are multiple enabled/active video tracks in a 
> MediaStream, the first active/enabled video track is the one that is 
> played in the video element. Users can then set the enabled attribute 
> to false, so that the video element falls back to the next available 
> video track. For this scenario it might also be nice to furnish a 
> "setEnabled" or "mute" API on the MediaStreamTrackList that takes a 
> single unsigned long index as a parameter and makes the track at that 
> given index enabled while disabling all other tracks.
>
This makes sense to me, but shouldn't we just leave this to the spec in 
the <video> specification?
It seems to be obvious enough how to read that when the input is a 
MediaStream.

              harald