Debian has a very strict policy on free and legal software. This helps keep everyone honest, but sometimes a pragmatic approach is called for. MP3 is a file format that is patent encumbered - but also in universal use.
I could use the supplied Ogg Vorbis tools but then my music wouldn’t work everywhere I want it to.
So I want to install Lame which is only available in source.
Download and extract
install a build environment by pulling in the build dependencies for something useful (I chose php)
sudo apt-get build-dep php5 sudo aptitude install fakeroot
check build dependencies of lame
and install them
sudo aptitude install nasm libsndfile1-dev chmod 700 debian/rules dpkg-buildpackage -rfakeroot -uc -b sudo dpkg -i ../lame_3.98.1_i386.deb ../libmp3lame0_3.98.1_i386.deb