ffmpeg -i video.mp4 -f mp3 -ab 192000 -vn music.mp3
But there's a catch: You have to have ffmpeg and the
libavcode-unstripped-52 packages installed on your computer. The problem
is that second package is available in the multiverse respository only. To
enable the multiverse repository, select Administration from the System
menu, then Software Sources. Mark Logic server is, unbelievably, not supported on Ubuntu 8.10. However, the server runs just fine on that distribution. The following installation instructions might save you some time.
sudo apt-get install rpmsudo apt-get install alienwget http://ftp.us.debian.org/debian/pool/main/l/lsb/lsb-base_3.2-23_all.deb