Apple's audio and video framework for the Macintosh, introduced in 1991 with the Mac System 7 operating system. QuickTime is the underlying engine in QuickTime Player, the media player that comes with QuickTime, as well as iTunes. There are numerous applications that support QuickTime authoring. QuickTime originally used Apple's proprietary codecs, but Cinepak, Sorenson and other codecs were added, and QuickTime supports third-party plug-ins. For example, Flip4Mac (www.telestream.net) provides QuickTime playback of the Windows Media Video (WMV) format. Also available for Windows, QuickTime is often downloaded by Windows users as many websites feature QuickTime movies. For years Apple and Microsoft did not support each other's formats; however, QuickTime Player later supported the Windows AVI format (but not all encoding methods), and Windows Media Player generally plays QuickTime movies. A Very Comprehensive Format A QuickTime file can contain any kind of continuous motion data such as audio, video, MIDI, animations, virtual reality, Karaoke text and time-based control information. Its time-based synchronization is a major feature, and QuickTime files can even be used to control external events such as lighting. QuickTime files use .QT, .MOV and .MOOV extensions. MPEG-4 and H.264 Because the QuickTime format was designed for ease of editing, it was chosen as the basis for the MPEG-4 container format. In reciprocation, Apple added MPEG-4 in QuickTime 6 and H.264 (based on MPEG-4) in QuickTime 7. See MPEG. QuickTime X In 2009, along with the debut of Mac OS X 10.6 (Snow Leopard), which was a major upgrade to 64 bits, QuickTime was also upgraded to 64 bits and given a higher numerical version (X=10) than the existing Version 7. Mac users have QuickTime X, while Windows users kept QuickTime 7. If a movie requires a 32-bit codec, components in QuickTime 7 are used. See iTunes, Windows Media and H.264.