extracting mp3s from youtube's videos

install the unplug plugin for firefox

install mencoder
$sudo apt-get install mencoder

download the video with unplug (right click and choose the unplug from menu)
in my case i have this video
extract the mp3 from the flv (audio is MP3-encoded in the movie file)
ffmpeg -i doors_when_the_music_is_over.flv -vn -acodec copy doors_when_the_music_is_over.mp3


The audio codec "copy" tells ffmpeg to use the same codec for encoding as was
used for decoding. Also, since we're not overriding any of the other audio
parameters such as sample rate or bit rate, we should be retrieving the sound
track exactly as it was multiplexed into the movie file.

you can read more about working with ffmpeg