How To Play Proprietary Format Media Files in Ubuntu

Because these formats require proprietary software to play them and this software is not free in the GPL sense, this cannot be provided in the Ubuntu distribution for legal reasons and requires downloading and installing.  This is straightforward in Ubuntu 7.04 (Feisty Fawn) and later but a bit more complicated in earlier versions.  This is covered later.

All versions from 7.04 (Feisty Fawn) inclusive (including 8.10)

The following method was used with a new installation of Feisty Fawn (v7.04) - Gutsy Gibbon is much the same but slightly simpler.  Hardy Heron (v8.04 LTS) is similar but with the GStreamer plugins in 2 files rather than 3.
  
When you try to play proprietary format files (such as MP3) in a media player you will get an error pop-up asking Search for suitable codec?  Click Yes.
An Add/Remove Applications window appears showing 3 lots of GStreamer plugins with a checkbox beside each to mark for download and installation. See Screenshot-1
Click in the check box and a popup window appears saying Restricted Software.  See Screenshot-2  After reading the conditions click OK.
Back in the Add/Remove Applications window - repeat for the other two to be sure of being able to play all file formats.  Now click Apply > Apply the following changes See Screenshot-3 click Apply there too to download and install the packages.  See Screenshot-4  A Changes applied box will appear when complete.
Back in the Add/Remove Applications, click OK.  The MP3 or other proprietry format file should now play.
Other formats such as WMA music files and MPG, AVI and WMV video files should play too
  

Older versions of Ubuntu

    The above didn't work on older versions and I used Medibuntu, Community support for these formats but you have to add the repository yourself.  Here is a quote from the appropriate documentation :-

Medibuntu (Multimedia, Entertainment & Distractions In Ubuntu) is a repository of packages that cannot be included into the Ubuntu distribution for legal reasons (copyright, license, patent, etc).

Adding the Repositories
    The following actions require use of the command line using a terminal window.  See Command Line in Using Ubuntu.  Command line entries are shown in red.  These may be copied from here and pasted into a Terminal window to avoid typos.  Make sure you include everything, including the - (minus or dash).
First, add Medibuntu's gpg key to your system's list of trusted APT keys.
wget -q http://medibuntu.sos-sts.com/repo/medibuntu-key.gpg -O - | sudo apt-key add -
Next, add Medibuntu's external sources.list. Make sure to use the correct sources.list that corresponds to your current distribution.
sudo wget http://medibuntu.sos-sts.com/sources.list.d/feisty.list -O /etc/apt/sources.list.d/medibuntu.list
Finally, update APT's package information to acquire information about packages in the Medibuntu repository.
sudo apt-get update

Trying to play file formats such as WMA, MP3 and MPG or WMV in the media player should produce a request to install the missing codecs much like the instructions above - follow the prompts to install.

Updated 27 October 2008