Fluendo mp3 decoder
Note that for MP3 in particular, Fluendo has made available a free (as in beer) codec, with a free (as in speech) implementation with a paid up license for the Gstreamer code framework. This requires execution of a license agreement for redistribution; unfortunately, the agreement does not permit sub-licensing, so while including it would be convenient and OLPC may choose to execute this agreement in the future, those redistributing our software would still have to execute this agreement to legally redistribute the codec.
In order to download the codec you have to "check out" the Fluendo mp3 decoder from their store for $0.00. You are then allowed to download the file fluendo-mp3-2.i386.tar.bz2
Installation
Follow the instructions above to obtain the fluendo-mp3-2.i386.tar.bz2 file. Unzip it, then copy the libgstflump3dec.so file into $HOME/.gstreamer-0.10/plugins on your local system. If you have root access you can instead copy it to /usr/lib/gstreamer-0.10. If you use this second position then the plugin will be available to any user logging into this machine.
Once it is copied over verify that gstreamer recognise their precence by doing a 'gst-inspect-0.10 flump3dec'.
Unless this command reports back 'No such element or plugin 'flump3dec' the plugin should be sucessfully installed and you should have access to playing back MP3 files using GStreamer applications