Re: [rtcweb] CNAMEs and multiple peer connections

Martin Thomson <> Thu, 13 March 2014 16:53 UTC

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Date: Thu, 13 Mar 2014 09:53:46 -0700
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From: Martin Thomson <>
To: Magnus Westerlund <>
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Subject: Re: [rtcweb] CNAMEs and multiple peer connections
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On 12 March 2014 01:29, Magnus Westerlund
<> wrote:
> I like to point out that the agreement and what is documented in
> rtp-usage is that WebRTC endpoint will have to make forwarded streams
> appear as locally originated. However, this as currently written does
> not apply to RTP middleboxes that interconnects multiple PeerConnections
> to form a multi-party session. This is deliberate to ensure that RTP
> topologies like RTP mixer and SFM do work on the RTP/RTCP level.

I'm still not clear on whether a middlebox interoperating with a
WebRTC endpoint is obligated to respect these rules or not.  I had
assumed that WebRTC is such a bully that they would be forced to.

> I am especially interested to know how you will "easy to apply manually"
> the synchronization. Can you please describe that. Because, that either
> requires an API call to tell the media framework, please consider the
> following CNAMES as equivalent, or some other method of telling the
> media framework that these different MST are actually originating from a
> common clock base.
In WebRTC, this would be:

var audio = pc1.getRemoteStreams()[0].getAudioTracks()[0];
var video = pc2.getRemoteStreams()[0].getVideoTracks()[0];
var synchronizedStream = new MediaStream(audio, video);

We'd have to say that this implies a statement about the clock base of
the tracks being the same.  ... and that this statement could be

As far as it goes, I'm sure that other systems could build a similar
function, but none of those are standardized.

> I protested about this, not to lower the users privacy, but over the
> concern that this was raised without providing a case where it was
> obvious that the user's privacy was impacted. Martin, you said that you
> would think about it, and the next statement was lets change it, without
> providing any motivation why the concern was significant.

I'm sorry about that, I thought about it, but didn't want to waste
everyone's time (mine included) with an essay on the subject.