File Format

QuickTime Movie File Format Specification, May 1996

File Format

A QuickTime file is simply a collection of atoms. QuickTime does not impose any rules about the order of these atoms.

Figure 0-3 depicts a typical QuickTime file.

Figure 3 The structure of a QuickTime file

In file systems that support file name extensions, QuickTime file names typically have an extension of ".mov" . On the Macintosh platform, QuickTime files have a file type of "MooV" . On the Macintosh, the movie atom may be stored as a Macintosh resource using the Resource Manager. The resource has a type of 'moov' . All media data is stored in the data fork.

As previously discussed, QuickTime files consist of atoms, each with an appropriate atom type. A few of these types are considered basic atom types and form the structure within which the other atoms are stored. Table 0-1 lists the currently supported basic atom types.

Table 1 QuickTime file basic atom types
Atom type	Use
`'free'`	Unused space available in file
`'skip'`	Unused space available in file
`'mdat'`	Movie data--usually this data can only be interpreted by using the movie resource
`'pnot'`	Reference to movie preview data
`'moov'`	Movie resource

While it is true that QuickTime imposes no strict order on a movie's atoms, it is often convenient if the movie atom appears near the front of the file. For example, an application that plays a movie over a network would not necessarily have access to the entire movie at all times. If the movie atom is stored at the beginning of the file, the application can use the meta-data to understand the movie's content as it is acquired over the network.

The following sections describe each of these basic atom types in more detail, including descriptions of the atoms that each basic atom may contain.