<p>I'm trying to convert old QuickTime framework code to the 64-bit Cocoa-based QTKit on OS X, which means that I can't drop down to the straight C function calls at any time.  Specifically, I'm trying to find a way to write QuickTime VR movies with QTKit, as they require some special metadata to set the display controller.  How can I do this with QTKit?</p>

As far as I can tell from the QTKit Documentation there is not way to do this in straight QTKit cocoa calls.  You'll need to
do this using the Quicktime-C APIs
, which of course aren't available to 64-bit applications.
I've run into issues like this numerous times when trying to convert a 32-bit app that uses Quicktime into a 64-bit app.  Here's hoping that Quicktime X will have a more fully featured QTKit set of APIs.