i believe i read somewhere that the DivX tools were being used by Factor 5 to play cinematics in real-time... maybe so clips from Star Wars movies can be played at the same time that a cut scene is rendered around it?
(eg. luke watching R2D2 play the clip of Princess Leia, all done with polygons, but the clip is from the movie)
i thought i also read somewhere that a video could be placed onto polygons or something, like a texture, with this kind of compression. i dunno, i hope i didn't dream that info but it may be possible.