What's the name of my sound card driver's file? I want to run fuser to determine what process is using my sound card, but I don't know what file to use. I ran fuser on /System/Library/Extensions while playing a YouTube video, but did not see any process IDs.
If you have an idea of which process is making the sound, you might be able to try them until you find it.  For example, QuickTime Player, when playing a movie, does not use any subprocesses.  Similarly iTunes when it is playing a song.  

On OS X 10.7 Lion, I did the following:  


open Activity Monitor, 
switch to "All Processes, Hierarchically"
found the application process I wanted and clicked it, 
clicked Inspect
clicked Open Files and Ports