Download and install, and voila you can see MP42 video in QT. Of course as noted in the readme and elsewhere you may have trouble getting the audio portion of your movie but that has nothing whatsoever to do with this codec. I'm not sure what the first reviewer here (Abe, who also posted the same comment on the MPEGv41 decoder) was trying to do when labeling both these codecs as "useless".. its just a thin wrapper around ffmpeg after all and ffmpeg does wonders.