Base Media Info Atoms

QuickTime Movie File Format Specification, May 1996

Base Media Info Atoms

The base media info atom, contained in the base media information atom, defines the media's control information, including graphics mode and balance information. Figure 0-26 shows the layout of a base media info atom.

Figure 26 The layout of the base media info atom

The base media info atom contains the following data elements.

Size: A 32-bit integer that specifies the number of bytes in this base media information header atom.
Type: A 32-bit integer that identifies the atom type; this field must be set to ' gmin' .
Version: A 1-byte specification of the version of this base media information header atom.
Flags: A 3-byte space for base media information flags. Set this field to 0.
Graphics mode: A 16-bit integer that specifies the transfer mode. The transfer mode specifies which Boolean operation QuickDraw should perform when drawing or transferring an image from one location to another.
Opcolor: Three 16-bit values that specify the red, green, and blue colors for the transfer mode operation indicated in the Graphics mode field.
Balance: A 16-bit integer that specifies the sound balance of this media. Sound balance is the setting that controls the mix of sound between the two speakers of a computer. This field is normally set to 0. See Inside Macintosh: QuickTime for more information about QuickTime sound balance values.
Reserved: Reserved for use by Apple. Set this field to 0.

For comprehensive details on transfer modes and opcolors and their values in QuickDraw, see Inside Macintosh: Imaging .