Recently I came across a video clip that I wanted to rip the audio from. Easy enough (and fast!) using mencoder:

mplayer -novideo -ao pcm:file=output.wav input_file.avi Then if you want to convert said wave file into an mp3 or ogg file: lame -b 64 -a output.wav new_output.mp3 oggenc --downmix -b 64 output.wav -o new_output.ogg