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

Media Data Atom TypesHint Mediasample descriptions to play at specific times, changes that affect those parts of the original track or mediamake those hints invalid. Changes to a movie that do not invalidate existing hint tracks include flattening(when there are no edit lists), and adding new tracks. Changes that invalidate hint tracks include:●●●●Flattening (when there are edit lists)Adding or deleting samplesChanging a track’s time scaleChanging sample descriptionsWarning Hint tracks are marked as inactive, so calling the FlattenMovie function with theflattenActiveTracksOnly bit set deletes all hint tracks from a movie.Packetization Hint Media Header AtomIn QuickTime movies, the media information atom ('minf') contains header data specific to the media. Forhint tracks, the media header is a base media information atom ('gmhd'). The hint track must contain the basemedia information atom.Hint Track User Data AtomEach hint track may contain track user data atoms that apply to only to the corresponding hint track. Thereare currently two such atoms defined.●User data atom type 'hinf'.This contains statistics for the hint track. The 'hinf' atom contains child atoms as defined in Table 4-17 (page254). In some cases, there are both 32-bit and 64-bit counters available. Any unknown types should be ignored.●User data atom type 'hnti'.This may contain child atoms. Child atoms that start with 'sdp ' (note, again, the space) contain SDP text forthis track. Text from these child atoms must be inserted into the proper place in the SDP text for the movie,after any common SDP text. This is analogous to the movie-level 'hnti' atom.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.253