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[whatwg] Media negotiation (RE: Peer-to-peer communication, video conferencing, and related topics (2))

From: Stefan Håkansson LK <stefan.lk.hakansson@ericsson.com>
Date: Tue, 29 Mar 2011 15:35:29 +0200
Message-ID: <BBF498F2D030E84AB1179E24D1AC41D612066B0DC7@ESESSCMS0362.eemea.ericsson.se>
> > > > !The web application must be able to    !If the video 
> is going to be displayed !
> > > > !define the media format to be used for !in a large 
> window, use higher bit-    !
> > > > !the streams sent to a peer.            
> !rate/resolution. Should media settings!
> > > > !                                       !be allowed to 
> be changed during a     !
> > > > !                                       !session (at 
> e.g. window resize)?      !
> > > 
> > > Shouldn't this be automatic and renegotiated dynamically via SDP 
> > > offer/answer?
> >
> > Yes, this should be (re)negotiated via SDP, but what is 
> unclear is how 
> > the SDP is populated based on the application's preferences.
> 
> Why would the Web application have any say on this? Surely 
> the user agent 
> is in a better position to know what to negotiate, since it 
> will be doing 
> the encoding and decoding itself.
The best format of the coded media being streamed from UA a to UA b depends on a lot of factors. An obvious one is that the codec used is supported by both UAs.... As you say much of it can be handled without any involvement from the application.

But let's say that the app in UA a does "addStream". The application in UA b (the same application as in UA a) has two <video> elements, one using a large display size, one using a small size. The UAs don't know in which element the stream will be rendered at this stage (that will be known first when the app in UA b connects the stream to one of the elements at "onaddstream"), so I don't understand how the UAs can select a suitable video resolution without the application giving some input. (Once the stream is being rendered in an element the situation is different - then UA b has knowledge about the rendering and could somehow inform UA a.)

Stefan
Received on Tuesday, 29 March 2011 06:35:29 UTC

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