Visit the mplayer web site
Scroll down to binary codecs packages and select the package for your linux system. Download and extract the files to the mplayer codecs directory.
If your mplayer is recent, this would be /usr/local/lib/codecs or /usr/local/lib/win32
if using an old version of mplayer.
These codecs plays the latest windows
media files,quicktime, realplayer and others.