Hmm... Seems to me that libquicktime on Mac OS X should just be a compatibility layer, adapting lqt calls to real, native QuickTime calls. The lqt codecs wouldn't require much attention at all, then. Have any pointers to which API calls you would actually use?
for decoding, have a look at modules/pdp_qt.c in the tarball (http://zwizwa.fartit.com/pd/pdp/) the encoder object is in yves' pidip lib (http://ydegoyon.free.fr/) in modules/pdp_rec.c
Then again, why not a native QuickTime external, perhaps based on QuickTimeTcl (once it's more stable...)?
since it just decodes the video (and audio) for a specific frame, and converts to the internal format, a native object is probably easier indeed. conversion are in the pdp framework (system/pdp_llconv.c ; not entirely mmx free yet..)
tom