[AG-TECH] AGN Audio Lip Sync

John I Quebedeaux Jr johnq at lsu.edu
Tue Sep 16 11:24:52 CDT 2003


We've had issues in the past with a packet shaper on our campus that 
caused a similar problem.... except that each of my video streams had 
various stages of... lag (up to a minute behind)... including the 
audio. There was always one on time, the rest were at various stages 
behind. I had to work with my telecom folks to 1) convince them there 
was a problem, 2) convince them there was a problem, 3) convin... you 
get the idea. Once I convinced them it took them 15 minutes to reset 
the shaper to allow my traffic through without being delayed. I had to 
drag them up to the AG node room for them to SEE it happening. Then the 
lightbulbs went off.

The symptom for us was that it worked fine within campus but going 
in/out (I don't recall which now, it was in one direction only) of 
campus was when we had the problem.

-John Q.

-- 
John I. Quebedeaux, Jr.
Computer Manager / Louisiana Biomedical Research Network
LSU Biological Sciences / 131 Life Sciences
e-mail: johnq at lsu.edu / web: http://lbrn.lsu.edu
phone: 225-578-0062 / fax: 225-578-2597

On Tuesday, September 16, 2003, at 10:04  AM, Brian Corrie wrote:

>
>
>
>  From:John I Quebedeaux/johnq/LSU at newmic.com on 09/16/2003 08:04 AM MST
>
>
>
>
>
>
>  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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