How can I extract audio track from video file and save it as MP3?

Very simple CLI solution:

ffmpeg -i VIDEOFILE -acodec libmp3lame -metadata TITLE="Name of Song" OUTPUTFILE.mp3

In case you don't have ffmpeg installed:

sudo apt-get install ffmpeg

You can do this in VLC.

Once you have started VLC:

1. select "Media" --> "Convert/Save"
2. Click "Add..." and select the file you want
3. Click "Convert / Save" (on the bottom)
4. Provide a "Destination file:"
5. Select the "Profile" (i.e. "Audio - MP3", "Audio - Vorbis (OGG)", etc.)
6. Click "Start"
7. Relax and enjoy your shoes

You can install VLC from Synaptic or the Software Center.

avidemux can do this.

It is inside Ubuntu Software Center or you can install it from the command line with:

sudo apt-get install avidemux