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Re: [rtcweb] Reasons not to multiplex audio with video (Re: Fwd: I-D Action: draft-rosenberg-rtcweb-rtpmux-00.txt)

Matthew Kaufman <matthew.kaufman@skype.net> Mon, 25 July 2011 13:05 UTC

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From: Matthew Kaufman <matthew.kaufman@skype.net>
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Date: Mon, 25 Jul 2011 09:04:56 -0400
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To: Harald Alvestrand <harald@alvestrand.no>
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Subject: Re: [rtcweb] Reasons not to multiplex audio with video (Re: Fwd: I-D Action: draft-rosenberg-rtcweb-rtpmux-00.txt)
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On Jul 25, 2011, at 8:06 AM, Harald Alvestrand wrote:

> On 07/24/11 16:44, Matthew Kaufman wrote:
>> In all my reading today I have not been able to find anything more concrete than the "SHOULD NOT" in section 5.2 of RFC3550. PLEASE follow up if you are aware of any other relevant specifications that would argue against using SSRC to multiplex audio and video streams over a single RTP session between a pair of compatible endpoints that agree to do so.
> I have found *one* reason not mentioned in the draft:
> 
> An RTP session with both "audio" and "video" media types cannot be represented by an SDP description, since SDP ties RTP sessions 1-1 to the "m" line of the description, which contains the top-level type, and the codec descriptions omit the top-level type in their codec naming.
> 
> I've said elsewhere that I consider this to be a design mistake for entirely different reasons, but this debate has reinforced my opinion that it is.

Good point, but perhaps it just argues for either A) not using SDP or B) extending SDP if we use it for RTCWEB (we probably need to do that anyway if we use SDP, given all the discussion about "hints" that we want to send from one end to the other)

Matthew Kaufman

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