Chunk Offset Atoms

QuickTime Movie File Format Specification, May 1996

Chunk Offset Atoms

Chunk offset atoms identify the location of each chunk of data in the media's data stream. Chunk offset atoms have an atom type of 'stco' . The chunk offset atom (shown in Figure 0-41 ) contains a table of offset information.

Figure 41 The layout of a chunk offset atom

The chunk offset atom contains the following data elements.

Size: A 32-bit integer that specifies the number of bytes in this chunk offset atom.
Type: A 32-bit integer that identifies the atom type; this field must be set to 'stco' .
Version: A 1-byte specification of the version of this chunk offset atom.
Flags: A 3-byte space for chunk offset flags. Set this field to 0.
Number of entries: A 32-bit integer containing the number of entries in the chunk offset table.
Chunk offset table: A chunk offset table consisting of an array of offset values. There is one table entry for each chunk in the media. The offset contains the byte offset from the beginning of the data stream to the chunk. The table is indexed by chunk number--the first table entry corresponds to the first chunk, the second table entry is for the second chunk, and so on.

Figure 0-42 shows an example of a chunk offset table

Figure 42 An example of a chunk offset table