hehe, I was going to sugest ffmpeg too. Damn I would wish the day whould be 36hours instead of 24h, it's not enough time for work, school, home and the various projects I work on and fs2. Cause I would really like to work on this on fs2_open (the movie support). But if you already done something into this direction I guess that would result in duplicated work.
I was thinking, the main problems whould be:
1. decoding the frames (use ffmpeg for that)
2. displaying them (as I can see there is a lot of stuff to read about all this formats to package the video information, other than RGB that is, but I think because fs2 already portably uses OpenGL then we could use OpenGL functions to display the movie frames

)