you can use AtomicParsley, a command line based open source tool to add metadata and artwork to your MPEG-4 files. On OS X you can use macports to install the tool.
example for an AtomicParsley call:
AtomicParsley 'Simpsons - Chili.m4v' --artist Simpsons --title 'Homer and the Chili' --album 'Simpsons, Season 6' --artwork Simpsons.jpg --stik 'TV Show' --TVShowName Simpsons --TVEpisode 605 --TVEpisodeNum 6 --TVSeasonNum 5 --description 'Homer attends a hot chili competition.'