Totem uses the xine libraries, not mplayers. If you use mandrake, I'm pretty sure you can get these from plf if you have urpmi set up. Otherwise, google for xine codecs and see what you get.
There are some codecs here:
http://cambuca.ldhs.cetuc.puc-rio.br/xine/
But I don't think thats quite what you're looking for. Good luck