that's just how the movies are stored in RoC and TFT, they're not real .mpq's, they're just renamed .avi's. If you chage they're name back to .avi they run in windows media player
Maybe rename the file to w3x instead of mpq and use it as a normal map?
I don't know, but I renamed a cinematic mpq to an avi, and yes it played completely fine. This is good to know :).