Chunk offset atom ('stco')
An atom that identifies the location of each chunk of data in the media’s data stream.
Overview
Chunk offset atoms have an atom type of 'stco'.
The chunk-offset table gives the index of each chunk into the containing file. There are two variants, permitting the use of 32-bit or 64-bit offsets. The latter is useful when managing very large movies. Only one of these variants occurs in any single instance of a sample table atom.
Note that offsets are file offsets, not the offset into any atom within the file (for example, a 'mdat' atom). This permits referring to media data in files without any atom structure. However, be careful when constructing a self-contained QuickTime file with its metadata (movie atom) at the front because the size of the movie atom affects the chunk offsets to the media data.
The layout of a chunk offset atom is as follows.
Chunk offset atom data field | Bytes |
|---|---|
4 | |
Type = | 4 |
1 | |
3 | |
4 | |
Variable |
Topics
Data fields
See Also
Describing samples
Sample table atom ('stbl')Seeking with a QuickTime fileSample description atom ('stsd')Time-to-sample atom ('stts')Creating video tracks at 30 frames per secondCreating video tracks at 29.97 frames per secondCreating sound tracks at 44.1 kHzComposition offset atom ('ctts')Composition shift least greatest atom ('cslg')Using composition offset and composition shift least greatest atomsSync sample atom ('stss')Partial sync sample atom ('stps')Sample-to-chunk atom ('stsc')Referencing two data files with a single trackSample size atom ('stsz')