Quicktime will do this (File/Export) but I think you will have to use QT Pro. QT Pro is the same download of QT only you enter a code to unlock some of the features, available from Apple for 20 bucks or on the internet if you know where to look.
You could also try MPEG Streamclip from www.squared5.com as that can convert various formats (I use it to put MPEGs into an iPod compatible format.)
By way of return, did you ever get your MacMAME problem sorted? I double click on the MacMAME application but nothing happens. I have even tried running the French version which seems to come with an installer but nothing happens.