Quicktime File Format (2012-08-14).pdf

Movie AtomsTrack Atoms●●To contain modifier tracks (tweens, and so forth).To contain packetization information for streaming protocols (hint tracks). Hint tracks may contain referencesto media sample data or copies of media sample data. For more information about hint tracks, refer to“Hint Media” (page 251).Note A QuickTime movie cannot consist solely of hint tracks or modifier tracks; there must be atleast one media track. Furthermore, media tracks cannot be deleted from a hinted movie, even ifthe hint tracks contain copies of the media sample data—in addition to the hint tracks, the entireunhinted movie must remain.Figure 2-6 (page 56) shows the layout of a track atom. Track atoms have an atom type value of 'trak'. Thetrack atom requires a track header atom ('tkhd') and a media atom ('mdia'). Other child atoms are optional,and may include a track clipping atom ('clip'), a track matte atom ('matt'), an edit atom ('edts'), a trackreference atom ('tref'), a track load settings atom ('load'), a track input map atom ('imap'), and a userdata atom ('udta').2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.55