The replays saved by MBAC I believe are just a list of the inputs entered - the game recreates the match by literally running the fight again with the exact same attacks done at the exact same time. It's not video, so you can't upload it on youtube or whatever.
I used to record matches, but I don't remember what I used. I think it was Camstudio (not Camtasia Studio - this is more legal free) and Virtualdub for a few quick post-processing-things, and then threw it into MediaCoder to use a codec that's not awful. I don't remember it well enough to give you exact directions, though, and Virtualdub is a bit of a confusing jerk, so you might want to find something a bit more intuitive.