How to Enable MP3 on Ubuntu 9.10
By Daniel D'Agostino, 2010-02-09
Introduction
On free Linuxes such as Ubuntu, MP3 playback is not supported by default. To enable it, you have to download a package containing non-free software (including the MP3 codec), and to do this, you first have to set the correct repository.
Medibuntu Repository
Follow the instructions on this page to set up the Medibuntu repository. Basically, it's System -> Administration -> Software Sources -> Other Software tab -> Add... button and paste:
deb http://packages.medibuntu.org/ karmic free non-free
Download ubuntu-restricted-extras package
Open a terminal and run the following command:
sudo apt-get install ubuntu-restricted-extras
You should now be able to play mp3s.