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Re: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization

Jonathan Lennox <jonathan@vidyo.com> Fri, 08 February 2013 15:59 UTC

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From: Jonathan Lennox <jonathan@vidyo.com>
To: Eric Rescorla <ekr@rtfm.com>
Date: Fri, 08 Feb 2013 10:59:30 -0500
Thread-Topic: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization
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Subject: Re: [rtcweb] Proposal for dealing with CNAMEs and MSIDs for synchronization
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On Feb 7, 2013, at 2:22 PM, Eric Rescorla wrote:

> Here's what I was trying to say at the microphone.
> 
> 1. When two MSTracks are in the same MediaStream on the sending side:
>  They must generate the same MSID in SDP and the same CNAME in RTP.

Note that, as a consequence of this -- if the same MediaStreamTrack is put into two different MediaStreams of the same PeerConnection, the sending side will need to synchronize all the tracks of those two MediaStreams together, and give them all the same CNAME.  (Because synchronization is transitive.)

If Stefan's proposal is accepted (i.e., all the tracks from a single endpoint are synchronized, period), this may come for free, at least for locally-generated tracks.  But if it isn't, this is a subtlety that may not be fully appreciated.

--
Jonathan Lennox
jonathan@vidyo.com

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