[AG-TECH] AGN Audio Lip Sync

Brian Corrie brian.corrie at newmic.com
Tue Sep 16 10:04:56 CDT 2003


When a lip synch is noticed, always the first solution is to restart rat. It
does tend to drift over time. The size of the drift in the time you mention
seems rather large. That is a bit odd. We see this occasionally if we leave
things on over long periods of time, but it is certainly not consistent (we
don't seem to degrade as a direct function of time).

I am not sure why the sync slippage occurs (don't know enough about rat/vic
and the RTP encoding) so I can't diagnose why you are seeing what you see.
The only thing that pops into my head is that if there is packet loss it may
have some impact (the protocols are supposed to handle that, but...). Also,
computationally, if the vic or rat processing can't keep up and falls behind
this may be the culprit. I can't remember if we see lag in the video or in
the audio in our case. With UDP and RTP, one would think that this would not
happen (you would just see packet loss instead) but again I am not sure...

That probably didn't help much did it 8-)

Brian


> -----Original Message-----
> From: Wachtel, Robert L [mailto:Robert.Wachtel at mso.umt.edu]
> Sent: Tuesday, September 16, 2003 7:23 AM
> To: ag-tech at mcs.anl.gov
> Cc: Christensen, Scott A
> Subject: [AG-TECH] AGN Audio Lip Sync
> 
> 
> Are there any recommended solutions to the following audio video
> synchronization difficulty?
> 
> Symptom: A progressively increasing sync delay between the video and
> audio received from other sites within a venue. Lip sync is very close
> when initially entering a venue, and then consistently the audio is
> progressively delayed behind the video. After an hour uptime we can
> notice a difference of up to 3 seconds. If we kill and 
> restart just the
> rat, the sync will be restored and then begin slipping again.
> 
> System:
> AGN 1.2
> Audio Box: Monarch AMD dual processor 4GB RAM, Creative Audigy sound
> card, Red Hat Linux 7.3 OS
> Video Display: Monarch AMD dual processor 4GB RAM, Matrox G450 x4 MMS
> quad head display card, Windows 2000 Pro OS
> 
> Local Network:
> 100Mb Switched to desktop
> 1Gb Campus backbone
> 
> Any suggested solutions or additional diagnostic measures would be
> appreciated.
> 
> Thanks,
> Bob Wachtel
> Director
> Presentation Technology Services (PTS)
> The University of Montana
> Missoula, MT 59812
> Phone: 406-243-2857
> FAX: 406-243-2689
> 



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