[gst-devel] comfort noise generation bin

[Olivier Crête]

On Mon, 2010-04-26 at 18:49 -0500, pl bossart wrote:
> > Oops, I though rtpjitterbuffer would generate a lost packet message
> > after a certain amount of time, but it seems to only generate it on the
> > next packet after a gap. So you are right, it is not a good solution.
> 
> I am not sure if this is the same mechanism, but the g72xdepay
> elements mark the first buffer after a talk burst as DISCONT as per
> the RTP spec. However this is somewhat unusable for the decoder since
> there are no indicators of the start of the silence part...

I don't think the decoder should be generating CNG without getting a SID
frame, otherwise we may end up getting CN when we really had packet
loss. So the start isn't too hard to guess. The problem is that the
every decoder then needs to have a thread started when a CN packet is
received that will generate the frames until it is stopped. And then the
decoder may not know it should really stop if the use switched codecs
during a silence period.

> 
> > I still think we need some kind of arbitration to not have more than one
> > decoder produce silence since Farsight2 will keep the previous decoders
> > if the sender starts sending on a new PT. That's why I wanted to do it
> > as late as possible (in the mixer).
> 
> Comfort Noise is generated mainly so that the receiver doesn't think
> the line is dead. Granted, if this is a multi-party call the need for
> CNG is less important. Chances are someone will be talking.
> Nevertheless, the decision to go to SID frames is made by each
> transmitter, the receiver can't do much in terms of arbitration:
> either you support CNG or you don't....

I guess maybe the decoder could just set GST_BUFFER_FLAG_GAP
on the CNG buffers. Then the mixer can be made to ignore buffers that
have this flag set.


-- 
Olivier Crête
olivier.crete at collabora.co.uk
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