$ sudo apt-get install ffmpeg
now cd in the terminal to the folder your video file that you want to convert is in then simply enter
$ ffmpeg -i YourVideoFile.flv -ab 160k -ac 2 -ar 44100 -vn YourAudioFile.mp3
and wait for it to convert :) yep it really is that simple.
the -i simply means your input file, the -ab indicates the bit rate, -vn means no video ouput, -ac 2 means 2 channels and the -ar 44100 indicates the sampling frequency.
You can edit these to suit your needs
