So I have had mythtv working for a while, then all of a sudden 2 weeks ago the sound stopped working in mythtv. I was able to play sounds with a command line utility, but there was no sound from mythtv. I had mythtv set to play from the default sound device and hadn't changed anything there.
After trying lots of things I eventually reinstalled ubuntu (yes I know, desperate times!) and sound was working again. However after a couple of days it stopped!
One thing I noticed is that when the sound was working, there were the following ALSA entries in myth's frontend log:
While now that sound stopped working it changed to an error about not finding the mixer:2012-03-23 21:13:39.785 AO: Opening audio device 'default' ch 2(2) sr 48000 sf signed 32 bit reenc 0
2012-03-23 21:13:39.786 ALSA, Error: Setting hardware audio buffer size to 6016
2012-03-23 21:13:39.786 ALSA, Error: Error opening /proc/asound/card0/pcm0p/sub0/prealloc: Permission denied.
2012-03-23 21:13:39.786 ALSA, Error: Try to manually increase audio buffer with: echo 6016 | sudo tee /proc/asound/card0/pcm0p/sub0/prealloc
2012-03-23 21:13:39.786 ALSA, Error: Unable to sufficiently increase ALSA hardware buffer size - underruns are likely
2012-03-23 21:13:39.788 AudioPlayer: Enabling Audio
So it seems to me that the default ALSA sound device as detected by mythtv has changed. Why would this happen?2012-03-23 22:14:39.716 AO: Opening audio device 'default' ch 2(2) sr 48000 sf signed 16 bit reenc 0
2012-03-23 22:14:39.718 AudioOutput Warning: mmap not available, attempting to fall back to slow writes
2012-03-23 22:14:39.761 ALSA, Error: no playback control PCM found on mixer device default
2012-03-23 22:14:39.761 ALSA, Error: Unable to open audio mixer. Volume control disabled
2012-03-23 22:14:39.761 AudioPlayer: Enabling Audio