Referencing Two Data Files With a Single Track

QuickTime Movie File Format Specification, May 1996

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Referencing Two Data Files With a Single Track

The data reference index to be used for a given media sample is stored within that sample's sample description. Therefore, a track must contain multiple sample descriptions in order for that track to reference multiple data files. A different sample description must be used whenever the data file changes or whenever the format of the data changes. The sample-to-chunk atom determines which sample description to use for a sample.

The sample description atom would contain the following data values:

Atom size	...
Atom type	`'stsd'`
Version/Flags	0
Number of entries	2
	Sample description size[1]	...
	Data format	`'tmcd'`
	Reserved	0
	Data reference index	1
	(sample data)	...
	Sample description size[1]	...
	Data format	`'tmcd'`
	Reserved	0
	Data reference index	2
	(sample data)	...

If there were only 1 sample per chunk and the first 10 samples were extracted from sample description 2 and the next 30 samples were extracted from sample description 1, the sample-to-chunk atom would contain the following data values:

Atom size	40
Atom type	`'stsc'`
Version/Flags	0
Number of entries	2
First chunk[1]	1
Samples per chunk[1]	1
Sample description ID[1]	2
First chunk[2]	11
Samples per chunk[2]	1
Sample description ID[2]	1

The data reference atom would contain the following data values:

Atom size	...
Atom type	`'dinf'`
	Atom size	...
	Atom type	`'dref'`
	Version/Flags	0
	Number of entries	2
	Size[1]	...
	Type[1]	`'alis'`
	Version[1]	0
	Flags[1]	0 (not self referenced)
	Data reference[1]	[alias pointing to file #1]
	Size[2]	...
	Type[2]	`'alis'`
	Version[2]	0
	Flags[2]	0 (not self referenced)
	Data reference[2]	[alias pointing to file #2]

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