This plugin contains elements necessary for doing RTjpeg compression and
decompression, as well as conversion from RGB to YUV and back, based
entirely on functions supplied by RTjpeg.c.

You can find RTjpeg at Justin Schoeman's site:
http://www.ee.up.ac.za/~justin/bttv/

The idea is to start out with the code elements reading and writing YUV420
images, with external elements to do the conversion.  Eventually (when
typing is a bit more sane/globally used) the codec elements will
automatically convert images to/from the proper format based on what their
peer wants to be dealing with.