some codecs don't work very well when RR resizes/manipulates the video window from media player classic. That's the case for some earlier versions of the ffmpeg codec for instance.. I always recommend installing DivX, XviD, Windows Media Codecs and whatever other direct show filters you want to use (i.e. Real Audio/Quick Time/etc), but all separate.. once you load one of the codec "packs" you never know what the heck they're doing. a lot of the times even if you uninstall them they still manage to screw up the settings to where it prevents the normal codecs from working.