[xiph-rtp] Speex -02 feedback and m bit question.

[Phil Kerr]

Hi Greg/Jean-Marc,

You have probably seen Colin Perkins' feedback on the AVT list regarding 
the -02 Speex draft.  Having it move to WG status for the next revision 
is great news!

One of Colin's questions:

> The use of the M bit in the RTP header to indicate comfort noise is  
> unusual. Can you comment why it was used in this way, rather than 
> being  used to indicate the first packet after the "silence" period, 
> as would  be typical? The unusual semantics are not necessarily 
> problematic, but  we I'd like to understand what benefit we gain from 
> the additional  complexity of atypical usage. 

 From the draft we specify:

   The M bit indicates if the packet contains comfort noise.  This field
   is used in conjunction with the cng SDP attribute and is detailed
   further in section 5 below.  In normal usage this bit is set if the
   packet contains comfort noise.

..

      cng:   comfort noise generation - either 'on' or 'off'.  If off
      then silence frames will be silent; if 'on' then those frames will
      be filled with comfort noise.

Should this really conform strictly to the RTP specs or is this a case 
where the RTP transportation needs to bend towards the encoder?

I think his other points, fixing the p bit and moving the ITU related 
text to the speex.org site are fair and should pose no problems.

Cheers

Phil