You could do it a few ways. Using mplayer the command would look like:
Code:
mplayer -vc null -vo null -ao pcm ./filename.avi
This will create a WAV file named "audiodump.wav" that contains the audio of the video file.
With ffmpeg, the command would look like:
Code:
ffmpeg -i ./filename.mpg -f mp3 audio_filename.mp3
This will dump directly to MP3, which may be better for you.