I've heard that
mplayer -dumpaudio -dumpfile out.mp3 file.flv
Works for extracting the audio from a video clip. It coredumped on my system, but the following did work:
mplayer npsh_ponytail_thatgo_640med.mov -novideo -ao pcm
lame audiodump.wav npsh.mp3
For the most awesome video by Natalie Portman's Shaved Head Sophisticated Sideways Ponytail.