QuickTime X

QuickTime X, released on August 28, 2009 with Mac OS X 10.6, is the 64-bit successor to the classic 32-bit releases of QuickTime. It was pre-installed with versions of macOS prior to 10.15 (Catalina). Windows is not supported, with 7.7.9 being the last version for PCs.

QTKit
QuickTime X used the QTKit framework, which was supported from Mac OS X 10.4.6 (Tiger) until 10.14.6 (Mojave). It phased out support for 32-bit codecs used by QuickTime 7 and earlier. QTKit was itself superseded by AVKit, which was introduced as part of AV Foundation in 2011 for Mac OS X 10.7 (Lion).