What is blocking my sound?

[Marc Shapiro <marcnshap@gmail.com>]

I am running Lenny, with alsa and udev.  Frequently then sound on my 
system just stops working.  When it does, I run the following command to 
check if the sound device is in use, or there is some other cause:

	'aoss play ~/public_html/footpain/media/montoya.wav

Usually, as the following output shows, the device cab not be opened:

	ALSA lib pcm_dmix.c:996:(snd_pcm_dmix_open) unable to open slave
	play soxio: Can't open output file `default': cannot open audio
	device

Usually the fix is to close all instances of Firefox until I find the 
culprit, and sound returns.  I just killed all running instances of 
firefox and can not think what else could have grabbed the device and 
not released it.  Is there a way to determine what process is using the 
device so that I can kill the appropriate thread instead of using trial 
and error?

Thanks for any ideas.

--
Marc Shapiro