I downloaded it and extracted the files into the required folder. As you asked, I reinstalled MPlayer. Nothing happened. I got the same error. Are you sure that I installed that in the right folder? I installed using an RPM.
MPlayer has to be recompiled from the source when new codecs are added. I am not sure how the rpm build was built but it looks like it was not configured to use all of the codecs. YOu will need to download the source from MPlayer and build it according to the directions in the README.
Here is an extract from the README. May I know what $prefix is?
$prefix is the install directory you pass to the ./configure when you build from the source. You would define it with
the default is '/usr/local' which is used if no prefix is given.