QTKit is an Objective-C interface to QuickTime available on Tiger, and also available with QT7 on Panther. It supercedes the Cocoa classes NSMovieView and NSMovie with a larger set of classes which provide a comprehensive interface into QuickTime from Objective-C. In addition to basic playback and tweaking, QTKit allows full-blown editing and other such goodies.
QTKit is also the name of an open-source wrapper around QuickTime that was made outside of Apple. For information on that wrapper, see the QTKitOSS page.
Apple’s QuickTime Kit Programming Guide: http://developer.apple.com/documentation/QuickTime/Conceptual/QTKitProgrammingGuide/index.html
Apple’s QuickTime Kit Programming Reference: http://developer.apple.com/documentation/QuickTime/Reference/QTCocoaObjCKit/index.html
Apple’s QTKit Frequently Asked Questions, with lots of juicy code snippets for some of the less obvious tasks: http://developer.apple.com/technotes/tn2005/tn2138.html
Here is a list of QTKit-related pages on this site: [Topic]