Did you know? Did I knew? I needed to extract the audio from a flash movie. Quite simple right? So why took it 2 minutes my first time? Because I forgot the no interest in video switch. I found this one on http://howto-pages.org/ffmpeg/#strip
# -vn : video kill switch
ffmpeg -i video.flv -vn -acodec copy audio.mp3
That -acoder copy still puzzles me. It is a copy the audio codec. But my flash movie had a mp2 codec. Is that a problem for mp3 players?