Sync sample atom ('stss')
An atom that identifies the key frames in the media.
Overview
In a media that contains compressed data, key frames define starting points for portions of a temporally compressed sequence. The key frame is self-contained — that is, it is independent of preceding frames. Subsequent frames may depend on the key frame.
The sync sample atom provides a compact marking of the random access points within a stream. The table is arranged in strictly increasing order of sample number. If this table is not present, every sample is implicitly a random access point.
Sync sample atoms have an atom type of 'stss'. The sync sample atom contains a table of sample numbers. Each entry in the table identifies a sample that is a key frame for the media. If no sync sample atom exists, then all the samples are key frames.
The layout of a sync sample atom is as follows.
Sync sample atom data field | Bytes |
|---|---|
4 | |
Type = | 4 |
1 | |
3 | |
4 | |
Variable |
Topics
Data fields
See Also
Describing samples
Sample table atomSeeking with a QuickTime fileSample description atomTime-to-sample atomCreating video tracks at 30 frames per secondCreating video tracks at 29.97 frames per secondCreating sound tracks at 44.1 kHzComposition offset atomComposition shift least greatest atomUsing composition offset and composition shift least greatest atomsPartial sync sample atomSample-to-chunk atomReferencing two data files with a single trackSample size atomChunk offset atom