iTunes 10.4 is now AV Foundation based, not QT http://tinyurl.com/3b2auaj
As I’ve written before, AV Foundation is the modern media playback framework for OS X. Originally developed for iOS and OS X it came to OS X with Lion, but Final Cut Pro X uses it, even on Snow Leopard (where AV Foundation is installed as a private framework in 10.6.7 and 10.6.8).
I think Apple are sending a strong message that QuickTime – as a framework for applications to use to play media – is not the way of the future. Particularly if you want a 64 bit application. While many parts of QT have been rewritten with a 64 bit wrapper as QTkit, the future is clearly away from QuickTime on OS X.
In fact, the use of QuickTime has been fading over the last decade as Apple moved to H.264/AAC in an MP4 wrapper for distribution purposes early last decade.
And now another of Apple’s media-rich applications appears to be built on AV Foundation now, instead of QuickTime, only falling back to use old QT codecs not supported under AV Foundation.