The OSX realplayer codec available at
http://www.mplayerhq.hu/MPlayer/releases/codecs/rp9codecs-macosx-20041107.pkg.zip
installs to /usr/local/lib/codecs. MPlayerOSX cannot
use the codec when it's there. By moving (or linking)
/usr/local/lib/codecs to /usr/local/lib/mplayer,
mplayer can find and use the real player codecs.