The Motion Pixels Movie Player is the only media player that properly handles the Motion Pixels codecs. Unfortunately it is years out of date and doesn't work properly under DirectX.
The Motion Pixels codec is done completely in software, no hardware acceleration of any kind is done. (Which makes it work with very crappy video card)s. But it just isn't as good as hardware accelerated video is. It is primarily used by SIRIUS in their MovieCD line of Video Discs. But it has also been used in several Windows 3.1 video games for the opening sequence videos. It is for the most part a dead technology now.
Windows Media Player will play Motion Pixels format video files if The Motion Pixels Movie Player is installed on the system. It doesn't support a few of the Motion Pixels specific features. But it is a whole lot better than the buggy Motion Pixels Player ever was.
The Flask MPEG video tools can convert a Motion Pixels codec movie into a DIVX codec movie. With a compression rate of well over 90 percent. This requires the Motion Pixels Player to be installed also.