Wednesday, December 31, 2014

HDMI Audio in Mythbuntu

My adventure replacing my old Mythbuntu box with a new one continues. It's been working for a while now, in terms of waking when it should, recording and replaying shows. Yesterday's immediate concern was sound. The PC hooks to my TV via an HDMI cable. While both live TV and recordings viewed through MythTV worked fine (including sound), applications run outside MythTV (such as VLC) had no sound.

As usual, Google was both my friend and my enemy -- it found lots of results for all of my search queries, most of which sent me off chasing wild geese. For some reason, Application > Settings > Settings Manager in Mythbuntu does not provide anything to configure sound, and installing the unity-control-center package did not remedy that. (I wonder if they block it to prevent users from configuring something that conflicts with the MythTV audio settings, which you set when configuring the MythTV front end?) I ran alsamixer and unmuted S/PDIF, but that did not fix things.

I did notice at some point that the configuration for ALSA (the sound system) at the operating system level seemed to default to PulseAudio. I read somewhere that MythTV, which uses ALSA, might kill the PulseAudio service to avoid conflicts with ALSA. That suggested either creating a configuration file for ALSA that avoids PulseAudio or configuring PulseAudio properly. I tried the latter and it worked. The steps were:
  1. Install the pavucontrol package from a repository.
  2. Run pavucontrol in a terminal.
  3. In the Configuration menu, choose the correct output device (in my case, "HDMI").
  4. Exit, cross fingers, reboot and test.
The fix may not be perfect. It works -- both MythTV and the VLC player (run from the desktop) have sound -- but I now get system error messages when I exit MythTV, which I was not getting before. The error messages are not specific (something unnamed apparently crashed), and I haven't poked through the logs. So far, the errors have not coincided with an perceptible loss of functionality, so they're just an annoyance. I can't be positive they are due to the sound fix, but they started immediately after it.