QuickTime Streaming

Hint Track Samples

Hint track samples either contain or point to the data to be sent in each packet. Hint track samples are not part of the hint track atom structure, although they are usually found in the same file. Use the hint track data reference atom ('dref' ) and sample table atom ('stbl' ) to find the file specification and byte offset for a particular sample.

The hint track structure is generalized to support hint samples in multiple data formats. The data format of a hint track sample is specified by the data format field of the sample description atom ('stsd' ). Currently, only the data format type of 'rtp ' is defined. Note that the fourth character in the type field is an ASCII blank (hex 20). Hint track samples are not atoms, and do not contain size or type fields. The type is found in the sample description, and the size is found in the sample table.

This section describes hint track samples in 'rtp ' data format.

Each hint track sample is used to generate one or more RTP packets.
All packets in a sample have the same RTP timestamp, which is also the hint sample time.
Each sample contains a packet table with one entry for each packet to be sent.
Each entry in the packet table contains RTP header and sequence information for a particular packet, as well as a data table.
The data table has one entry for each of block of contiguous data that belongs in the packet.
A typical packet is constructed from more than one block of data. A typical data table might have an entry for a small block of data contained in the data table itself, a second entry pointing to data in another hint track sample, and a third entry pointing to data in a media sample.

Bear in mind that media samples may not reside in the same file or resource as hint track samples. You locate media samples in the same way you locate hint track samples, by walking the media track atom structure and using the data reference atom ('dref' ) and sample table atom ('stbl' ) found there.

Note also that hint track samples may not have a one-to-one correspondence to packets or media samples. A packet may contain several small media samples, and a large media sample may be broken into several packets.

Hint track sample data is byte-aligned, but not necessarily 32-bit aligned. Hint track sample data is always in big-endian format.

Table 3 Hint track sample format

Field	Bytes	Description
Entry count	2	16-bit integer specifying the number of entries in the packet table. Each entry specifies an RTP packet. A sample with an entry count of 0 must be skipped.
Reserved	2	Set to zero if creating. Ignore if using.
Packet table	variable	Each entry in this table specifies an RTP packet. Packet table entries contain data tables. See the packet table format below for more information.
Additional data	variable	If data table entries point to data stored in hint samples, that data is stored here.

Hint Track Samples

Packet Table Format

Extra Information TLV Table Format

Data Tables