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Re: [AVT] I-D ACTION:draft-ietf-avt-rtp-speex-01.txt

On 11 Jun 2007, at 20:50, Internet-Drafts at ietf.org wrote:
A New Internet-Draft is available from the on-line Internet-Drafts
directories.
This draft is a work item of the Audio/Video Transport Working Group of the IETF.

Title : RTP Payload Format for the Speex Codec
Author(s) : G. Herlein, et al.
Filename : draft-ietf-avt-rtp-speex-01.txt
Pages : 21
Date : 2007-6-11

Speex is an open-source voice codec suitable for use in Voice over IP
(VoIP) type applications. This document describes the payload format
for Speex generated bit streams within an RTP packet. Also included
here are the necessary details for the use of Speex with the Session
Description Protocol (SDP).

A URL for this Internet-Draft is:
http://www.ietf.org/internet-drafts/draft-ietf-avt-rtp-speex-01.txt

This looks to be in pretty good shape, the main issue being mapping parameters to the "a=fmtp:" line in SDP. Detailed comments follow:

Marker bit "to indicate that the RTP packet contains at least one complete frame" is unusual for audio (although typical for video). It would be better used to indicate first packet after a silent period, as is usual for audio codecs.

Section 3.3: "Sampling rate values of 8000, 16000 or 32000 Hz MUST be used. Any other sampling rates MUST NOT be used" is confusing. Better to say "The sampling rate MUST be either 8000 Hz, 16000 Hz, or 32000 Hz".

Section 4.1.1: "rate" needs to be listed a required parameter, since the codec supports several sampling rates.

Section 5: the "a=fmtp:" attribute is for media type parameters only. If you wish to define vbr, cng, and mode parameters, they must be defined as media type parameters in the IANA considerations, and then mapped into the "a=fmtp:" line. Section 6.2 of RFC 4749 is a good example of how to do this.

Cheers,
--
Colin Perkins
http://csperkins.org/



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