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QuickTime Streaming

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No Data

If the source field is 0, there is no data. Ignore the following 15 bytes. Insert no data into the packet for this entry.

Field	Bytes	Description
Source	1	Always 0
Unused	15	Padding

Immediate Data

If the source field is 1, the data is in the information field of this entry. There is a 1-byte data length field, followed by up to 14 bytes of data.

Field	Bytes	Description
Source	1	Always 1
Length	1	8-bit value indicating the number of data bytes that follow
Data	14	The number of data bytes indicated by the length field, plus any padding to equal 14 bytes

Sample Data

If the source field is 2, the data is in a track's data sample. The track is either the media track being hinted or the hint track itself.

Field	Bytes	Description
Source	1	Always 2
Track ref index	1	8-bit integer indicating the track reference by index
Length	2	16-bit integer specifying the number of bytes to copy
Sample number	4	32-bit integer specifying the sample number to copy the data from
Offset	4	32-bit integer specifying the byte offset into the sample at which to begin copying data
Bytes per compression block	2	16-bit unsigned integer specifying the number of bytes in a compression block, after compression. A value of 0 is equivalent to a value of 1.
Samples per compression block	2	16-bit unsigned integer specifying the number of uncompressed samples in a compression block. A value of 0 is equivalent to a value of 1.

Source

An 8-bit integer, value 2, indicating the data source is sample data

Track ref index

An signed 8-bit integer used to determine which track's sample data should be used. A value of 0 indicates that the hint track refers to one media track. The reference is stored in the hint track's 'tref' atom. Use that media track's sample data. A value of 1-127 indicates that the hint track refers to multiple media tracks. The references are stored in a table in the hint track's 'tref' atom. The value of the track ref index field indicates which entry holds the track ID of the media track whose samples should be used. A value of -1 (FF hex) indicates that the data resides in a sample in the hint track itself.

Length

A 16-bit integer specifying the number of bytes to insert into the packet

Sample number

A 32-bit integer specifying the sample number. Use the sample table atom ( 'stbl' ) in the indicated track to find the file specification and byte offset for this sample.

Offset

A 32-bit integer specifying where in the sample to begin copying the data from

Bytes per compression block

The number of bytes in a compression block, after compression. If this entry is 0 or 1, compression blocks are not used. See note below.

Samples per compression block

The number of uncompressed samples contained in a compression block. If this entry is 0 or 1, compression blocks are not used. See note below.

Normally, the byte offset for a sample is calculated by determining the sample number within a chunk, then adding the size of the preceding samples in that chunk to the chunk offset. If multiple samples are stored in compression blocks, as is the case with compressed audio, the sample size cannot be used to determine the offset within the chunk. Once you have determined the sample offset (the zero-based sample number within a chunk), the byte offset is determined using this formula:

SO = sample offset (0 if first sample, 1 if second sample, and so on)
CO = chunk offset
BCB = bytes per compression block
SPC = samples per compression block
byte offset = (SO * BCB / SPC) + CO

As an example, GSM audio typically compresses 160 samples into a 33-byte block, so a sample from a GSM audio track would have a BCB of 33 and an SPC of 160. The 161st sample in a chunk would have a sample offset of 160, so the byte offset of the sample would be (160 * 33 / 160) plus the chunk offset.

Sample Description Data

If the source field is 3, the data is in a sample description atom ( 'stsd' ) either in the media track being hinted or in the hint track itself.

Field	Bytes	Description
Source	1	Always 3
Track ref index	1	8-bit integer indicating the track reference by index
Length	2	16-bit integer specifying the number of bytes to copy
Sample description index	4	32-bit integer specifying which entry in the sample description table to copy the data from
Offset	4	32-bit integer specifying the byte offset into the sample at which to begin copying data
Reserved	4	4 bytes that must be set to zero.

Source

An 8-bit integer, value 3, indicating the data source is a sample description.

Track ref index

An signed 8-bit integer used to determine which track's sample description should be used. A value of 0 indicates that the hint track refers to one media track. The reference is stoered in the hint track's 'tref' atom. Use that media track's sample description. A value of 1-127 indicates that the hint track refers to multiple media tracks. The references are stored in a table in the hint track's 'tref' atom. The value of the track ref index field indicates which entry in the 'tref' atom holds the track ID of the media track whose sample description should be used. A value of -1 (FF hex) indicates that the data resides in the sample description of the hint track itself.

Length

A 16-bit integer specifying the number of bytes to insert into the packet

Sample description index

A 32-bit integer specifying the sample description by index. Sample descriptions are table entries in a sample description child atom ( 'stsd' ) of a track's sample table atom ( 'stbl' ). The sample description index corresponds to the table entry for a sample description.

Offset

A 32-bit integer specifying the byte in the sample description from which to begin copying data.