From: http://unix.stackexchange.com/questions/6402/how-to-remove-an-audio-track-from-an-mp4-video-file
ffmepg -i INPUT.m4v -map 0:0 -map 0:1 -acodec copy -vcodec copy OUTPUT.m4v
Copies the first video channel “0:0″ and the first audio channel “0:1″ discarding the remaining streams.