IETF Logo Mail Archive

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

Emil Ivov <emcho@jitsi.org> Mon, 25 July 2011 12:17 UTC

Return-Path: <emil@sip-communicator.org>
X-Original-To: rtcweb@ietfa.amsl.com
Delivered-To: rtcweb@ietfa.amsl.com
Received: from localhost (localhost [127.0.0.1]) by ietfa.amsl.com (Postfix) with ESMTP id E041821F84BC for <rtcweb@ietfa.amsl.com>; Mon, 25 Jul 2011 05:17:29 -0700 (PDT)
X-Virus-Scanned: amavisd-new at amsl.com
X-Spam-Flag: NO
X-Spam-Score: -3.487
X-Spam-Level:
X-Spam-Status: No, score=-3.487 tagged_above=-999 required=5 tests=[AWL=0.113, BAYES_00=-2.599, RCVD_IN_DNSWL_LOW=-1]
Received: from mail.ietf.org ([64.170.98.30]) by localhost (ietfa.amsl.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id 9yd4bSKWWVRS for <rtcweb@ietfa.amsl.com>; Mon, 25 Jul 2011 05:17:29 -0700 (PDT)
Received: from mail-ww0-f44.google.com (mail-ww0-f44.google.com [74.125.82.44]) by ietfa.amsl.com (Postfix) with ESMTP id B5FAF21F844F for <rtcweb@ietf.org>; Mon, 25 Jul 2011 05:17:28 -0700 (PDT)
Received: by wwe5 with SMTP id 5so2698604wwe.13 for <rtcweb@ietf.org>; Mon, 25 Jul 2011 05:17:27 -0700 (PDT)
Received: by 10.216.237.205 with SMTP id y55mr468529weq.49.1311596247644; Mon, 25 Jul 2011 05:17:27 -0700 (PDT)
Received: from porcinet.u-strasbg.fr ([2001:660:4701:1001:21e:c2ff:fe1b:2fe]) by mx.google.com with ESMTPS id b13sm4277798wbh.24.2011.07.25.05.17.26 (version=TLSv1/SSLv3 cipher=OTHER); Mon, 25 Jul 2011 05:17:26 -0700 (PDT)
Message-ID: <4E2D5ED5.5060706@jitsi.org>
Date: Mon, 25 Jul 2011 14:17:25 +0200
From: Emil Ivov <emcho@jitsi.org>
Organization: Jitsi
User-Agent: Mozilla/5.0 (Macintosh; U; Intel Mac OS X 10.5; bg; rv:1.9.2.18) Gecko/20110616 Thunderbird/3.1.11
MIME-Version: 1.0
To: Harald Alvestrand <harald@alvestrand.no>
References: <4E123C54.10405@jdrosen.net> <8785C0A3-31E5-44D7-8557-3BEEE4F95E3D@skype.net> <4E2D5C5D.6060402@alvestrand.no>
In-Reply-To: <4E2D5C5D.6060402@alvestrand.no>
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: quoted-printable
Cc: rtcweb@ietf.org
Subject: Re: [rtcweb] Reasons not to multiplex audio with video (Re: Fwd: I-D Action: draft-rosenberg-rtcweb-rtpmux-00.txt)
X-BeenThere: rtcweb@ietf.org
X-Mailman-Version: 2.1.12
Precedence: list
List-Id: Real-Time Communication in WEB-browsers working group list <rtcweb.ietf.org>
List-Unsubscribe: <https://www.ietf.org/mailman/options/rtcweb>, <mailto:rtcweb-request@ietf.org?subject=unsubscribe>
List-Archive: <http://www.ietf.org/mail-archive/web/rtcweb>
List-Post: <mailto:rtcweb@ietf.org>
List-Help: <mailto:rtcweb-request@ietf.org?subject=help>
List-Subscribe: <https://www.ietf.org/mailman/listinfo/rtcweb>, <mailto:rtcweb-request@ietf.org?subject=subscribe>
X-List-Received-Date: Mon, 25 Jul 2011 12:17:30 -0000

На 25.07.11 14:06, Harald Alvestrand написа:
> 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 am not sure I understand this. Why would one need to use the same "m"
line? What would be the consequences of using two different "m" lines?

Personally, I am still not convinced that multiplexing brings
significant improvement over the status quo but if we accept it then it
definitely needs to keep separate "m" lines for tons of reasons.

Emil


-- 
http://jitsi.org

v2.23.0 | Report a Bug | By Email