[mythtv-users] Note to people seeing buffer underruns and have choppy playback

Jean-Yves Avenard jyavenard at gmail.com
Wed Mar 9 01:37:34 UTC 2011


Hi

This was particularly true for users of Live! audio card.

I have just backported some changes to fixes/0.24 that hopefully will
resolve those issues for good.

Additional information is available in the commit log:
https://github.com/MythTV/mythtv/commit/b41e2182b34832f29becceb52a795d67bbd0bdd7

or in the MythTV wiki for troubleshooting guide:
http://www.mythtv.org/wiki/Troubleshooting:Prebuffering_pause#Audio_Issues

Note that the default buffer size allocated to ALSA by default is only
64kB; this isn't sufficient for most usage. Now the default will
depend on your distribution, it's 4096kB under Ubuntu for example.

If the buffer size allocated to ALSA isn't sufficient, you will see a
warning in the logs with something like:
"Unable to sufficiently increase ALSA hardware buffer size - underruns
are likely"

This will usually have just before a hint of what command you need to
run to increase this.
Like:
Try to manually increase audio buffer with: echo 128 | sudo tee
/proc/asound/card0/pcm1p/sub0/prealloc

128kB is now the minimum recommended for playing stereo, 16bits, 48kHz audio.

If playback is fine, and you suffer no choppiness or buffer underruns,
then you can safely ignore the message.

JY


More information about the mythtv-users mailing list