[xiph-rtp] Re: Speex -02 feedback and m bit question.
Jean-Marc.Valin at USherbrooke.ca
Thu Apr 14 15:14:36 PDT 2005
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".
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.
Jean-Marc Valin <Jean-Marc.Valin at USherbrooke.ca>
Universite de Sherbrooke
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