I needed to isolate the audio track from an HDV video I captured from my camera. This command worked great:

mplayer -dumpaudio video.m2t -dumpfile audio.mp3

as discussed here: http://linux.byexamples.com/archives/229/extract-audio-from-video-or-online-stream/

UPDATE: To extract wav audio data from a dv file, I had to use this command:

ffmpeg -i video.dv -vn -acodec copy audio.wav

Details here: http://www.tuxradar.com/content/ffmpeg-made-easy