upgrade to testing (Gnome): audio playback borked

[Jim McCloskey <mcclosk@ucsc.edu>]

After an upgrade to Debian testing this weekend (jan 23, 2010), audio
playback on my desktop GNOME machine was left in a compromised state.

None of the following worked following the upgrade (they worked before):

   VLC
   audacious
   exaile
   listen
   totem
   rhythmbox

By `not work' here, I mean that the application seems to think that it
is playing the sound-file (there is no error message), but no data is
actually sent to ALSA (as far as I can see), and nothing is therefore
audible. Watching the levels in the mixer (no activity at all)
suggests that no data is being directed to the sound-card.

It's not the case that ALSA is broken. The sound-card is properly
detected and registered in /proc/asound/cards; alsamixer works fine,
and the low-level command line utilities like aplay and mpg321 work
beautifully. Xine, mplayer, and its derivatives (smplayer, kmplayer,
gnome-mplayer) work very well.

With VLC and audacious(2), I was able to fix the problem by re-setting
their Output plugin from `Default' (which had worked before) to Alsa
or (in the case of VLC) to Pulseaudio or Jack.

That leaves:

   exaile
   listen
   totem
   rhythmbox

I suspect that what these have in common is that they use gstreamer as
their backend, suggesting that that is where the problem ultimately
lies. Gstreamer is installed on this system:

  gstreamer0.10-alsa  
  gir1.0-gstreamer-0.10
  gstreamer0.10-plugins-bad 
  gstreamer0.10-plugins-base 
  gstreamer0.10-plugins-good  
  gstreamer0.10-plugins-ugly 
  gstreamer0.10-pulseaudio  
  gstreamer0.10-tools 
  gstreamer0.10-x 
  libgstreamer-plugins-base0.10-0 
  libgstreamer0.10-0 
  phonon-backend-gstreamer

Has anyone seem similar problems, or am I uniquely privileged in
having to deal with this?

Oh, the joys of linux audio.

Jim