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

Movie AtomsSample AtomsData reference indexA 16-bit integer that contains the index of the data reference to use to retrieve data associated withsamples that use this sample description. Data references are stored in data reference atoms.These four fields may be followed by additional data specific to the media type and data format. See “MediaData Atom Types” (page 154) for additional details regarding specific media types and media formats.Time-to-Sample AtomsTime-to-sample atoms store duration information for a media’s samples, providing a mapping from a time ina media to the corresponding data sample. The time-to-sample atom has an atom type of 'stts'.You can determine the appropriate sample for any time in a media by examining the time-to-sample atomtable, which is contained in the time-to-sample atom.The atom contains a compact version of a table that allows indexing from time to sample number. Other tablesprovide sample sizes and pointers from the sample number. Each entry in the table gives the number ofconsecutive samples with the same time delta, and the delta of those samples. By adding the deltas, a completetime-to-sample map can be built.The atom contains time deltas: DT(n+1) = DT(n) + STTS(n) where STTS(n) is the (uncompressed) tableentry for sample n and DT is the display time for sample (n). The sample entries are ordered by time stamps;therefore, the deltas are all nonnegative. The DT axis has a zero origin; DT(i) = SUM (for j=0 to i-1 ofdelta(j)), and the sum of all deltas gives the length of the media in the track (not mapped to the overalltime scale, and not considering any edit list). The edit list atom provides the initial DT value if it is nonempty(nonzero).Figure 2-35 (page 101) shows the layout of the time-to-sample atom.Figure 2-35The layout of a time-to-sample atomBytesTime-to-sample atomAtom sizeType = 'stts'VersionFlagsNumber of entriesTime-to-sample table44134VariableThe time-to-sample atom contains the following data elements.2012-08-14 | © 2004, 2012 Apple Inc. All Rights Reserved.101