[mythtv-users] Re: Tips for fixing prebuffering pause and WriteAudio: buffer underrun

[Michael Carland]

--- SpikeyGG <spikeygg at hotmail.com> wrote:
> >From: Michael Carland <mcarland at yahoo.com>
> >
> >I seem to have all of my install mistakes corrected, except for one.
> >
> >When I play recorded content all is well. But when I play live TV, I
> get
> >many  "prebuffering pause" messages, and an occasional "WriteAudio:
> buffer
> >underrun". The video stutters during the prebuffering messages.
> >
> >I done some googling, and tried a few things, but have not been able to
> >get around this. I am looking for tips on how to find the source of the
> >problem.
> >
> >I have tried vmstat on both the frontend and the backend, and don't see
> >anything that stands out. No swapping, plenty of memory, at least 20%
> idle
> >cpu on both ends.
> >
> >I have the "Extra audio buffering" checked. I tried the "Aggresive
> >Soundcard Buffering", but it didn't help, so I turned it back off.
> >
> >I am using ALSA on the frontend, and other than the stutters, it sounds
> >fine.
> >
> 
> I have a similar problem:
> 
> I've found that when I use ALSA without the "Extra audio buffering" it
> gives 
> me lots of this:
> 2005-03-28 11:54:27.415 WriteAudio: buffer underrun
> 2005-03-28 11:54:28.202 WriteAudio: buffer underrun
> 2005-03-28 11:54:34.626 WriteAudio: buffer underrun
> 2005-03-28 11:54:34.924 WriteAudio: buffer underrun
> 2005-03-28 11:54:37.762 WriteAudio: buffer underrun
> The audio on certian channels is crackly and the video is jumpy.  You
> can 
> see from the timestamps that these babys fill up the logfile very
> quickly.
> 
> And if I enable the "Extra audio buffering" with ALSA it gives me lots
> of 
> this:
> 2005-03-28 11:56:04.449 prebuffering pause
> 2005-03-28 11:56:06.250 prebuffering pause
> 2005-03-28 11:56:07.685 prebuffering pause
> 2005-03-28 11:56:08.621 prebuffering pause
> 2005-03-28 11:56:09.637 prebuffering pause
> The audio skips ever so slightly and so does the video but it's better
> than 
> the buffer undderrun.  The prebuffering pause messages come once a
> second... 
> much slower than the underruns.
> 
> I haven't figured out how to fix either of these problems.  I'm running 
> MythTV from CVS, with a pcHDTV HD-3000 card.  Most of the time I just
> use 
> /dev/dsp but I've been wanting to use the ALSA because when I get a new 
> reciever I'll be using the ALSA digital option to send it out the
> optical 
> port.  Plus, I'd like to use a mixed audio driver so I never get caught
> with 
> the "audio device is in use" message.  My hardware is nForce3 built-in
> sound 
> on my motherboard.
> 
> Thanks,
> -Greg 

One thing I have noticed in the logs that are different between live tv
and playing recorded content. Live tv has:

2005-03-28 20:24:28.249 Using protocol version 14
2005-03-28 20:24:28.303 Using protocol version 14

in the logs, but recorded content does not. I perused the list archive
while I was waiting for my hardware to arrive, and remember reading
something about playing from NFS works better than playing over the Myth
protocol. I do have an NFS share/mount between the backend/frontend. Might
those protocol version 14 messages imply that live tv is using the
protocol for video transfer instead of NFS, and that is why live tv
doesn't work as well as playing prerecorded video?

-Michael



		
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