If Simion wasn't as knowledgeable as he is, I'd link you to the ZSNES board's video dumping guide.
I think the file should be called
merged.avi if you dump video/audio together. Might be different if you just dump video (maybe video.avi or movie.avi?), I don't remember...
Hey, I've gotta set up mEncoder on this new computer, so I'll refresh my memory in the process. Hopefully then I can help a bit more efficiently if you still need it - or perhaps I'll be the one having difficulties, and you can come to my rescue.