[mythtv-users] choppy playback on one network frontend fine of the other

[Rich West]

ryan patterson wrote:
> Hello all,
>
> I have a really annoying problem.  My main frontend now has horrible 
> choppy pauses whenever I try to watch something (worse on HD 
> recordings but alsso affects non-HD).  I really don't know why this is 
> happening.  I didn't change any hardware.  This has been a stable 
> system for over 12 months and it worked fine for weeks after upgrading 
> to mythtv 0.21.  I can use my second frontend without any problems.  
> So I don't think the issue is with the backend.
>
> Here are some details about my setup:
> all computers are running ubuntu 7.10 and mythtv 0.21 (I do not 
> compile it myself)
> dedicated backend -> duel intel  Xeon 2GHz
> dedicated frontend (has problems with playback) -> intel core 2 duo 
> 1.8GHz, nvidia Geforce 7600GS
> desktop with frontend (no problems with playback) -> intel pentimum D 
> 3GHz, nvidia Geforce 7800
>
> There does not seem to be any bottle necks that I can find.  The CPU 
> load on the frontend doesn't look critical during playback..  I have a 
> gigabit network which has been plenty fast for over a year.
>
> Here are some of the error messages mythfrontend outputs:
> 2008-04-30 21:56:27.977 NVP: prebuffering pause
> 2008-04-30 21:56:27.983 WriteAudio: buffer underrun
> 2008-04-30 21:56:29.357 NVP: Prebuffer wait timed out 10 times.
> 2008-04-30 21:56:30.397 NVP: prebuffering pause
> 2008-04-30 21:56:33.781 NVP: prebuffering pause
> 2008-04-30 21:56:33.789 WriteAudio: buffer underrun
> 2008-04-30 21:56:34.575 NVP: prebuffering pause
> 2008-04-30 21:56:34.581 WriteAudio: buffer underrun
> 2008-04-30 21:56:35.126 
> RingBuf(myth://192.168.0.210:6543/1051_20080430190000.mpg 
> <http://192.168.0.210:6543/1051_20080430190000.mpg>): Waited 1.0 
> seconds for data to become available...
> 2008-04-30 21:56:35.941 NVP: prebuffering pause
> 2008-04-30 21:56:38.562 WriteAudio: buffer underrun
> 2008-04-30 21:56:38.969 NVP: prebuffering pause
> 2008-04-30 21:56:38.970 WriteAudio: buffer underrun
> 2008-04-30 21:56:39.775 
> RingBuf(myth://192.168.0.210:6543/1051_20080430190000.mpg 
> <http://192.168.0.210:6543/1051_20080430190000.mpg>): Waited 1.0 
> seconds for data to become available...
> 2008-04-30 21:56:40.367 NVP: Prebuffer wait timed out 10 times.
> 2008-04-30 21:56:41.519 NVP: prebuffering pause
>
> Any ideas?

A couple...

Is it happening all of the time on this frontend or is it on again/off 
again?  What is the load average on the backend server?  What is the 
backend server doing at the time of the choppiness?

 From the backend server, what are the ping time results?  You *should* 
see sub millisecond responses.  If it is high (>15ms), then it might be 
a cabling problem.  First plug the frontend in to a different port on 
your gigE switch.  If that doesn't help, swap out the cable from the 
frontend to the switch.  If that still doesn't help, physically move 
your other frontend to the location of the problem frontend and see if 
the working frontend is experiencing any issues when connected to where 
the problem frontend was.

Some quick list searches come up with:
http://www.mythtv.org/pipermail/mythtv-users/2006-June/137956.html
http://threebit.net/mail-archive/mythtv-users/msg52276.html (describes 
what the prebuffering bit really means)
http://www.mythtvtalk.com/forum/viewtopic.php?t=3878&postdays=0&postorder=asc&start=20

-Rich