Try Subler:
http://code.google.com/p/subler/
It seems to be based on
MPEG4IP. There may be a GPAC/MP4Box GUI for OS X, but I'm not aware of one.
However, it's never too late to learn command line! It would make these things much easier since there are lots of platform-independent video tools that are mainly used through command line interfaces. In this case the commands themselves are quite simple and there are instructions all over the web.