[mythtv-users] WriteAudio: buffer underrun with HD content

Mr. Myth mythtv at blandford.net
Fri Jan 26 16:08:55 UTC 2007


I recently upgraded from 0.20 stable to 0.21-150_trunk_r12545 from 
atrpms to get my hdhomerun working with multiple NIC interfaces.  This 
is my first real attempt at doing HDTV on mythtv.

I have a split frontend/backend setup.

Watching SDTV with 0.20 ( and previous ) has always worked well on this 
hardware.  Under 0.21trunk, there are occasional pauses but nothing too 

However, when I try to watch any HDTV content either frontend machine it 
will play for about 3 seconds and then pause for 1 second.  It makes it 
completely unwatchable.  Here is the interesting parts of the frontend log.

2007-01-25 09:40:16.554 NVP: Prebuffer wait timed out 10 times.
2007-01-25 09:40:16.806 WriteAudio: buffer underrun
2007-01-25 09:40:19.265 NVP: prebuffering pause
2007-01-25 09:40:19.266 WriteAudio: buffer underrun.
2007-01-25 09:40:35.116 WriteAudio: buffer underrun
2007-01-25 09:40:35.210 WriteAudio: buffer underrun
2007-01-25 09:40:35.364 WriteAudio: buffer underrun
2007-01-25 09:40:35.526 WriteAudio: buffer underrun

The WriteAudio messages just continue as long as I try to play the video 

Mythfrontend is using 80% of the cpu while watching HDTV content.

If I play the same files with mplayer, they only use ~50% of the cpu and 
don't have any pausing or audio issues.

Any ideas or suggestions?  It if it related to the onboard sound, I am 
willing to add cards as the WAF is quickly moving towards 0%. 



More info:

The backend is a 3.6Ghz P4.  It does other duties as well as mythtv.  It 
also has a PVR-500.

One frontend is my desktop - a 2.4Ghz dual core with an NVidia 6600.  It 
uses the snd-hda-intel sound driver with stereo output.

My HTPC is a 3.2Ghz Athlon with an asus a8n-vm csm with on board NVidia 
6150.  It uses the snd-hda-intel sound driver with SPDIF coaxial output 
to my amp.

The NVidia driver is configured to use Option      "UseEvents" "true".  
This helped lower the cpu usage during playback but didn't help the 
pausing or audio issue.

I have tried enabling and disabling the extra audio buffering in 
mythtv.  It didn't seem to make any difference.

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