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

[Jean-Marc Valin]

Hi,

I haven't see the thread on the avt list, can you send me the link?

I'm not sure how the CNG is supposed to work. What I called cng in the
current draft is only about doing cng in the case of discontinuous
transmission (perhaps it could be renamed dtx_cng), so that when no
packets are sent, the decoder knows whether it should generate comfort
noise or just put zeros.

I don't know what the p bit is, so I can't comment on it. Same about the
"ITU related text".

	Jean-Marc

Le jeudi 14 avril 2005 à 23:00 +0100, Phil Kerr a écrit :
> 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
> 

-- 
Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca>
Universite de Sherbrooke