[pulseaudio-discuss] rtp question

[CJ van den Berg]

On Wed, Feb 20, 2008 at 05:15:39PM +0200, Tanu Kaskinen wrote:
> 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?

TBO, I wasn't aware that module-rtp-recv was supposed to be doing rate
compensation resampling. If it does, then my observations must have some
other explanation.

-- 
CJ van den Berg

mailto:cj at vdbonline.com
  xmpp:cj at vdbonline.com
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