Mplayer by default doesn't play *.rmvb files, which are real player files, probably because the codecs are proprietary and because of that they can't be packed in the Mplayer basic codec pack.
Basically in this "how to" we are going to show how to add a additional pack of codecs (Windows codecs), in which the RMVB codec is included.
First off all, let's start by installing the Mplayer, using apt-get:
$ sudo apt-get install mplayer
Now that the mplayer is installed let's download the the pack, at:
ftp://opensys.linuxpackages.net/pub/Slackware-10.1/jay/mplayer/MPlayer_codecs-20050412-i686-1jto.tgz
Extract the MPlayer_codecs-20050412-i686-1jto.tgz like this:
$ mkdir /tmp/codecs
$ cd /tmp/codecs
$ tar -zxvf /.../MPlayer_codecs-20050412-i686-1jto.tgz
Now we have all the extracted content of MPlayer_codecs-20050412-i686-1jto.tgz in /tmp/codecs.
The next step is to copy the codecs to the rigth place, so that Mplayer can use them,
that place is the directory /usr/lib/win32 (which probably doesn't exist). To do that just do like this:
$ sudo mkdir /usr/lib/win32
$ sudo cp /tmp/codecs/usr/lib/codecs/* /usr/lib/win32
And that's it, now you can play RMVB files along with many others.
Just one more thing, cleaning up the extracted codecs:
$ sudo rm -rf /tmp/codecs
All set! Enjoy :)
