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

[Aymeric Moizard <jack at atosc.org>]

On Tue, 12 Jun 2007, Colin Perkins wrote:

> > 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.

Right that is confusing.

Marker (M) bit: The M bit is set to one on the first packet received 
after a silent period.

> 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".

I agree.

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

agree too.

> 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.

But that's definitly what is being said in section 5: in the following
text, we wanted to inform that you MUST use a=fmtp for mode, vbr and cng:

   An other way to make recommendations to the remote Speex encoder is
   to use its specific parameters via the a=fmtp: directive.  The
   following parameters are defined for use in this way:

Would you advise to change it to this text?:

   An other way to make recommendations to the remote Speex encoder is
   to use its specific parameters via the a=fmtp: directive.  "mode",
   "cng" and "vbr" parameter MUST be specified using this directive. The
   parameters are defined for use in this way:

As I understand your comment, you mean that "mode", "vbr" and "cng" should
appear in the section "4.1.1.  Registration of media type audio/speex"? 
Right?

tks,
Aymeric MOIZARD / ANTISIP
amsip - http://www.antisip.com
osip2 - http://www.osip.org
eXosip2 - http://savannah.nongnu.org/projects/exosip/

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


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