Apple has been busily working to 64-bit-ify all of the frameworks they plan to continue supporting into the future (Snow Leopard and beyond). However, QuickTime is scheduled for some nice Cocoaification, so it didn’t get much 64-bit love. QTKit, the 64-bit impostor, pretends to be the 64-bit way forward, but unfortunately this is far from useful.
QuickTime is all C function stuff, rather verbose and boring. It’s also 32-bit only. The 64-bit front end on it is a framework called QTKit. However, 64-bit QTKit is little more than an impostor that secretly makes things messier during the 32-to-64-bit transition.