Media Atoms

QuickTime Movie File Format Specification, May 1996

Media Atoms

Media atoms define a track's movie data. The media atom contains information that specifies the media handler component that is to interpret the media data, and it also specifies the data references.

The media atom has an atom type of 'mdia' . It may contain other atoms, such as a media header ('mdhd' ), a handler reference ('hdlr' ), media information ('minf' ), and user data ('udta' ). The only required atom in a media atom is the media header atom.

Figure 0-18 shows the layout of a media atom.

Figure 18 The layout of a media atom

The handler reference atom tells you the kind of media this media atom contains--for example, video or sound. The layout of the media information atom is specific to the media handler that is to interpret the media. "Media Information Atoms," beginning on [link] , discusses how data may be stored in a media, using the video media format defined by Apple as an example.

Media atoms contain the following data elements.

Size: A 32-bit integer that specifies the number of bytes in this media atom.
Type: A 32-bit integer that identifies the atom type; this field must be set to 'mdia' .
Media header: The media header atom. This atom contains the standard media information. See the next section for details.
Media handler: The media handler atom. This atom identifies the media handler component that is to be used to interpret the media data. See "Handler Reference Atoms," beginning on [link] , for more information.
Media information: The media information atom. This atom contains media-type specific data for use by the media handler component. See "Media Information Atoms" for more information.
User data: The user data atom associated with this media. See "User Data Atoms" for more information.

Media Header Atoms

Handler Reference Atoms