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

["Alfred E. Heggestad" <aeh at db.org>]

Colin,

many thanks for your comments. see inline..

Colin Perkins wrote:
> 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.

fixed in my working copy of -02

I looked in some other RFCs/I-Ds and found this:

  http://www.ietf.org/rfc/rfc4749.txt
  "The M bit MUST be set to zero in all packets."

  http://www.ietf.org/internet-drafts/draft-ietf-avt-rfc3047-bis-04.txt
  "The M bit is set to zero."


> 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".

fixed in my working copy of -02


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

I assume that you mean "rate=sampling rate" here. Not sure how to formulate
it in the best way, but I ended up with this:


      rate: The sampling rate MUST be either 8000 Hz, 16000 Hz, or 32000
      Hz.



in other wideband codec specs I found this:


http://www.ietf.org/rfc/rfc4749.txt
"Required parameters: none"

http://www.ietf.org/internet-drafts/draft-ietf-avt-rfc3047-bis-04.txt

  Required parameters:

      bitrate: the data rate for the audio bit stream.  This parameter
      is mandatory because the bit rate is not signaled within the
      G.722.1 bit stream.  At the standard G.722.1 bit rates, the value
      MUST be either 24000 or 32000 at 16 Khz sample rate, and 24000,
      32000 or 48000 at 32 Khz sample rate.  If using the non-standard
      bit rates, then it is RECOMMENDED that values in the range 16000
      to 48000 be used.  Non standard rates MUST have a value that is a
      multiple of 400 (this maintains octet alignment and does not then
      require (undefined) padding bits for each frame if not octet
      aligned).


> 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.

thanks for this comment. I have moved the definition of the fmtp parameters
to the "IANA Considerations" section, which is then referenced from the
"SDP Usage" section.


unless there are any more comments, I will publish -02 within the next
few days.



/alfred

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


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