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Re: Tracks in multiple Stream . Re: Teasing apart the data API questions

From: Harald Alvestrand <harald@alvestrand.no>
Date: Thu, 17 May 2012 22:28:23 +0200
Message-ID: <4FB55F67.2010704@alvestrand.no>
To: Cullen Jennings <fluffy@cisco.com>
CC: Randell Jesup <randell-ietf@jesup.org>, public-webrtc@w3.org
On 05/17/2012 09:03 PM, Cullen Jennings wrote:
> Sure, that all makes sense along with the examples you and Harald raised but I should have been more precise in my original email. I'm talking about in the context of a single PeerConenction objects. In all these example there would still only need to be one of theses media streams added to a given PeerConenction object. So, I'm still at the same place of not seeing why we need this that I was when I started this thread...
So when you said

"I'd like to back up and talk about normal Tracks being attached to more 
than one stream."

you really meant whether it should be possible to have more than one 
track containing the same stream added to a single PeerConnection object?

That's not what I thought you were asking .... I really don't see the 
useful situation either, but OTOH adding such a restriction in the API 
seems quite difficult to me; we would have to specify that the AddStream 
of a PeerConnection object could fail if one of the tracks inside the 
stream is already attached to the same PeerConnection, which is a "late 

The way I think of the signalling now (NOTE: more comments on 
draft-alvestrand-rtcweb-msid always welcome!), it would be simple to 
represent on the wire; "just" allow multiple MSID values for the same 
SSRC, and send the track once.

Other details could be more complex.

> On Apr 23, 2012, at 3:30 PM, Randell Jesup wrote:
>> On 4/23/2012 5:08 PM, Harald Alvestrand wrote:
>>> On 04/23/2012 05:01 PM, Cullen Jennings wrote:
>>>> On Apr 15, 2012, at 6:42 , Harald Alvestrand wrote:
>>>>> B1: Should the data "channel" be similar to a MediaStreamTrack,
>>>>> including the ability to be part of one or more MediaStreams,, be
>>>>> connected to consumer entities, be muted, and so on?
>>>> I'd like to back up and talk about normal Tracks being attached to
>>>> more than one stream. I don't think this makes any sense and certainly
>>>> adds to implementation complexity. Lets say we have tracks A , B, and
>>>> C. And tow streams S1 and S2. If A and B are in S1, and B and C are in
>>>> S2, it effectively mens all three are synchronized so why not just
>>>> have all there in a single stream?
>>>> I am missing the use case for a single track in more than one stream.
>>> The classical example is when one uses GetUserMedia to get audio and
>>> video, and one wishes to extract only the video stream and show it in a
>>> preview element, while both the audio and video should be sent to the
>>> remote site via a PeerConnection.
>> Correct.  Or attach audio from a single mic to two media streams, one for the front camera and one for the rear.  And the two streams may have totally different destinations (different peerconnections, or local display per Harald).
>> -- 
>> Randell Jesup
>> randell-ietf@jesup.org
Received on Thursday, 17 May 2012 20:28:54 UTC

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