[AG-TECH] Audio and Video Syncronization

Lisa Childers childers at mcs.anl.gov
Tue Jun 26 20:36:58 CDT 2001


What version of rat and vic (both display and video capture) are you


-----Original Message-----
From: owner-ag-tech at mcs.anl.gov [mailto:owner-ag-tech at mcs.anl.gov]On
Behalf Of Will, Rodger (R.)
Sent: Tuesday, June 26, 2001 8:29 PM
To: 'Marty Hoag'
Cc: Ag-Tech (E-mail)
Subject: RE: [AG-TECH] Audio and Video Syncronization

If I leave and enter a room, it seems to sync better for a while.  However,
today I did this and the sync became worse.  Is packet loss the culprit?  I
have also seen misordered packets.  Will this throw off sync off also?

-----Original Message-----
From: Marty Hoag [mailto:Marty_Hoag at NDSU.NODAK.EDU]
Sent: Tuesday, June 26, 2001 9:21 PM
To: Will, Rodger (R.)
Cc: Ag-Tech (E-mail)
Subject: Re: [AG-TECH] Audio and Video Syncronization

   I always edit or ntp.conf to add a couple local servers because I figure
lower delay and variance is better and things should sync even if the remote
server is unreachable (more on that later).  However, I'm not sure how much
effect that will have on the actual audio/video syncronization.  I've had a
feeling that rat or vic can drift, especially if there is packet loss or
weirdness but others would know more about why that is.  I'd also check
like the rat settings to make sure everyone is at 16khz audio and look at
playout and decode stats for remote sites (but again, others may have more
reasons as to why the drift).

   One other thing about ntp.  There is an "ntpdate" command that is invoked
boot of the AGiB versions of the system that also points to
ntp-1.accessgrid.org.  This command initially sets the clock for the video
capture and audio capture machines.  Once in a while (maybe 1 in 10?
really measured) this fails because of a dns lookup error or something like
this.  Then, since we are on daylight time, xntpdc (which points to the
servers) conks out because the difference in time is greater than 3600 (like
3600.3 or something).  I suspect that the cmos clock is set to CST which is
hour off from CDT.  Anyway, when this happens we are all of a sudden running
hour off.  I'm not sure if there is any solution (customizing the ntpdate or
running it more than once each for a different server? ;-).

   Also, you can sync your display machine using w2k display machine (I
Bill Nickless first pointed this out).  From command line (may need to have
admin privs - not sure) you enter something like
   net time /setsntp:"ntp.host1.foo ntp.host2.foo ..."
where the ntp.host1.foo and ntp.host2.foo are local ntp servers (if just one
don't need the quote marks).  Then just go to the Administrative "Services"
entries, make sure the Windows Time Service is set to auto and start it.  I
found a description of this at

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