[pulseaudio-discuss] rtp question

Tanu Kaskinen tanuk at iki.fi
Wed Feb 20 07:15:39 PST 2008

On Wed, Feb 20, 2008 at 12:00:22PM +0100, CJ van den Berg wrote:
> RTP doesn't provide any kind of synchronisation, so the different
> machines will definitely drift. This is a much bigger problem that the
> different latencies. At least the latencies are constant. And yes, it
> will be very annoying. 
> > any experience with this?
> I've tried it once between two rooms at opposite ends of my house.  It
> started out with a slight reverb effect, which was pretty acceptable.
> But after about 3-5 minutes it was far enough out of sync that turned
> into an annoying echo effect.

Why does that happen? The source machine is pushing stuff to
the network at rate R1 and the receivers can do nothing
about it. Also the soundcard pulls audio from module-rtp-rcv
at rate R2. It's clearly wrong to assume that either clock
would actually tick at the rate it claims to tick, let alone
assuming that both would be accurate. So there must
resampling that compensates the difference between R1 and
R2. R1 is the same in all receivers, so if rate compensation
is done, the only thing that can cause sync problems between
receivers is their different internal latencies.

Doesn't module-rtp-recv do the resampling after all, or what
part have I understood wrong?

Tanu Kaskinen

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