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QuickTime Streaming

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The Generic Media Header Atom ( 'gmhd' )

The generic media header atom ( 'gmhd' ) contains a single child atom, the generic media information atom ( 'gmin' ). The information in this atom is not used by RTP servers, and can be ignored.

The Handler Description Atom ( 'hdlr' )

The handler description atom ( 'hdlr' ) found in the media information atom ( 'minf' ) contains information that is not used for hint tracks. It can be ignored by RTP servers.

Do not mistake the 'hdlr' atom in the media information atom ( 'minf' ) for the 'hdlr' atom in the media atom ( 'mdia' ). The 'hdlr' atom in the media atom identifies this track as a hint track. The 'hdlr' atom in the media information atom can be ignored.

The Data Information Atom ( 'dinf' )

The data information atom ( 'dinf' ) contains a single child atom: the data reference atom ( 'dref' ). The data reference atom contains a table of data references which are formatted like child atoms. These data references tell you where the hint track sample data can be found. Bear in mind that this is a reference to the hint track's data, not the data in the media track being hinted.

Media tracks can have their sample data spread across multiple files, so the data references are in table format, allowing multiple entries. A hint track will have a single data reference entry. This will normally be a reference of type 'alis' , which indicates a file reference. The reference can also be of type 'rsrc' , indicating that the data is stored in a resource file or the resource fork of a Macintosh file.

This is followed by a three-byte flag. The flag is normally set to 0x0001. This indicates that the hint track sample data is in the same file as the movie atom you are parsing. Note that this flag is set to 0x0001 even if the data is in a different fork of the same file.

If this flag is not 0x0001, it will be followed by a file specification in Macintosh alias format (see Inside Macintosh: Files ). This specifies the file that contains the hint track sample data.

If the data reference is of type 'rsrc' , a resource type (32-bit unsigned integer) and resource ID (16-bit signed integer) are appended. This resource contains the hint track sample data.