[whatwg] PeerConnection feedback

Stefan Håkansson LK stefan.lk.hakansson at ericsson.com
Wed Apr 13 04:35:19 PDT 2011


-----Original Message-----
From: Ian Hickson [mailto:ian at hixie.ch] 
Sent: den 12 april 2011 04:09
To: whatwg
Subject: [whatwg] PeerConnection feedback

>On Tue, 29 Mar 2011, Stefan H kansson LK wrote:
>> > > > > The web application must be able to define the media format to 
>> > > > > be used for the streams sent to a peer.
>> > > > 
>> > > > 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.)
>I had assumed that the video would at first be sent with some more or less 
>arbitrary dimensions (maybe the native ones), and that the receiving UA 
>would then renegotiate the dimensions once the stream was being displayed 
>somewhere. Since the page can let the user change the <video> size 
>dynamically, it seems the UA would likely need to be able to do that kind 
>of dynamic update anyway.
Yeah, maybe that's the way to do it. But I think the media should be sent with
some sensible default resolution initially. Having a very high resolution could
congest the network, and a very low would give bad user experience until the 
format has been renegotiated.


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