QuickTime 3 Reference

Structure of an Effect Description

An effect description is a QTAtomContainer , the general QuickTime structure for holding a set of QTAtoms . Each QTAtom in the effect description contains the value for a single parameter of the effect. All effect descriptions must contain the set of required atoms, which specify attributes such as which effect component will be used. In addition, effect descriptions can contain a variable number of parameter atoms , which hold the values of the parameters of the effect.

Each atom contains either data or a set of child atoms. If an atom contains data, the data is the value of the attribute or parameter, and this value remains constant while the effect executes. If the atom contains a set of child atoms, they should contain a tween entry and the value of the parameter will be interpolated for the duration of the effect.

For detailed information about creating and editing QTAtom and QTAtomContainer data structures, see Chapter 1, "Movie Toolbox." For more information about tweens, see "Tween Components and Native Tween Types" (page 1015) .

You assemble an effect description by adding the appropriate set of atoms to a QTAtomContainer data structure. You then add the entire description to the media of the video track that contains the effect. The effect description forms the sample for the media of the video track.