[AVT] Comments on draft-ietf-avt-rtp-ac3-04.txt
Magnus Westerlund <magnus.westerlund@ericsson.com> Mon, 30 May 2005 09:24 UTC
Received: from localhost.localdomain ([127.0.0.1] helo=megatron.ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1DcgVp-000659-OW; Mon, 30 May 2005 05:24:45 -0400
Received: from odin.ietf.org ([132.151.1.176] helo=ietf.org) by megatron.ietf.org with esmtp (Exim 4.32) id 1DcgVo-000654-8N for avt@megatron.ietf.org; Mon, 30 May 2005 05:24:44 -0400
Received: from ietf-mx.ietf.org (ietf-mx.ietf.org [132.151.6.1]) by ietf.org (8.9.1a/8.9.1a) with ESMTP id FAA29657 for <avt@ietf.org>; Mon, 30 May 2005 05:24:41 -0400 (EDT)
Received: from penguin.ericsson.se ([193.180.251.47]) by ietf-mx.ietf.org with esmtp (Exim 4.33) id 1DcgpA-0004M7-U4 for avt@ietf.org; Mon, 30 May 2005 05:44:46 -0400
Received: from esealmw129.eemea.ericsson.se ([153.88.254.120]) by penguin.ericsson.se (8.12.10/8.12.10/WIREfire-1.8b) with ESMTP id j4U9LtmS008236; Mon, 30 May 2005 11:24:37 +0200 (MEST)
Received: from esealmw129.eemea.ericsson.se ([153.88.254.177]) by esealmw129.eemea.ericsson.se with Microsoft SMTPSVC(6.0.3790.211); Mon, 30 May 2005 11:24:12 +0200
Received: from [147.214.34.60] ([147.214.34.60]) by esealmw129.eemea.ericsson.se with Microsoft SMTPSVC(6.0.3790.211); Mon, 30 May 2005 11:24:12 +0200
Message-ID: <429ADBBC.5020703@ericsson.com>
Date: Mon, 30 May 2005 11:24:12 +0200
From: Magnus Westerlund <magnus.westerlund@ericsson.com>
User-Agent: Mozilla Thunderbird 1.0.2 (Windows/20050317)
X-Accept-Language: en-us, en
MIME-Version: 1.0
To: avt@ietf.org, "Link, Brian" <BDL@dolby.com>
References: <200505271942.PAA20174@ietf.org>
In-Reply-To: <200505271942.PAA20174@ietf.org>
Content-Type: text/plain; charset="UTF-8"; format="flowed"
Content-Transfer-Encoding: 7bit
X-OriginalArrivalTime: 30 May 2005 09:24:12.0565 (UTC) FILETIME=[5762BC50:01C564F9]
X-Spam-Score: 0.0 (/)
X-Scan-Signature: d8ae4fd88fcaf47c1a71c804d04f413d
Content-Transfer-Encoding: 7bit
Cc:
Subject: [AVT] Comments on draft-ietf-avt-rtp-ac3-04.txt
X-BeenThere: avt@ietf.org
X-Mailman-Version: 2.1.5
Precedence: list
List-Id: Audio/Video Transport Working Group <avt.ietf.org>
List-Unsubscribe: <https://www1.ietf.org/mailman/listinfo/avt>, <mailto:avt-request@ietf.org?subject=unsubscribe>
List-Post: <mailto:avt@ietf.org>
List-Help: <mailto:avt-request@ietf.org?subject=help>
List-Subscribe: <https://www1.ietf.org/mailman/listinfo/avt>, <mailto:avt-request@ietf.org?subject=subscribe>
Sender: avt-bounces@ietf.org
Errors-To: avt-bounces@ietf.org
Hi Brian I have reviewed the updated version and basically think it is fine. However I have the following comments. I think only two are really significant and probably should be addressed or at least discussed before going to working group last call. 1. Clarification on how to determine when the next frame starts. I think one should add a sentence clarifying how one determines where the next frame begins in payloads with FT=0. After looking at the codec specification I determined from the bit-stream syntax that the "frmsizecod" in the syncinfo block provides this information for each frame. However I think one should point out that one actually on a payload depacketizer level has to go in and read these bits to determine the length of the AC-3 frame and thus determine where the next starts. I would suggest the following text to be added to section 4.1 after figure 4. "When receiving AC-3 payloads with FT=0 and more than a single frame (NF > 0), a receiver needs to use the "frmsizecod" field in the synchronization information (syncinfo) block in each AC-3 frame to determine the frame's length. That way a receiver can determine where the next frame will start." 2. The limitation on BSI in section 5.1. Why is BSI limited to not be greater than 8? As the RTP payload format provides the parameters to negotiate this if using offer/answer two peers can determine the highest BSI value supported by the receiver. Thus one could in the future use the same payload format for updated bit-stream formats as long as the do not violate the basic requirements this payload format is built on (frmsizecod field present, 5/8th is decodable). So please clarify if there is any problem you foresee with above proposal. Otherwise I would recommend that the following sentence is simply removed: "Values greater than 8 MUST NOT be used with this payload format." Editorial comments: E1: The bit-numbering in figure 3 is missalinged. Both the tens and single numbers needs one space in the beginning. E2. Section 5.1, Encoding consideration. Please remove the current two sentenced and replace it with "Framed". See section 4.8 in the following draft: http://www.ietf.org/internet-drafts/draft-freed-media-type-reg-04.txt E3. Section 7: I would like to reorder the text in the paragraph for better clarify. "The general congestion control considerations for transporting RTP data apply to AC-3 audio over RTP as well, see RTP [RFC3550], and any applicable RTP profile (e.g. [RFC3551]). AC-3 encoders may use a range of bit rates to encode audio data, so it is possible to adapt network bandwidth by adjusting the encoder bit rate in real time or by having multiple copies of content encoded at different bit rates. Additionally, packing more frames in each RTP payload can reduce the number of packets sent and hence the overhead from IP/UDP/RTP headers, at the expense of increased delay and reduced error robustness against packet losses." Cheers Magnus Westerlund Multimedia Technologies, Ericsson Research EAB/TVA/A ---------------------------------------------------------------------- Ericsson AB | Phone +46 8 4048287 Torshamsgatan 23 | Fax +46 8 7575550 S-164 80 Stockholm, Sweden | mailto: magnus.westerlund@ericsson.com _______________________________________________ Audio/Video Transport Working Group avt@ietf.org https://www1.ietf.org/mailman/listinfo/avt
- [AVT] I-D ACTION:draft-ietf-avt-rtp-ac3-04.txt Internet-Drafts
- [AVT] Comments on draft-ietf-avt-rtp-ac3-04.txt Magnus Westerlund