QuickTime 4 Reference

Structure of an Input Map

The input map contains a set of atoms that refer to the tracks used as sources for the effect. Each source track is represented by one track reference atom of type kTrackModifierInput .

Each modifier input atom contains two children, one of type kEffectDataSourceType , and one of type kTrackModifierType , which hold the name and type of the source.

The name of the source is a unique identifier that you create, which is used in the effect description to reference the track. Any four-character name is valid, as long as it is unique in the set of source names.

Important
Apple recommends you adopt the standard naming convention 'srcX' , where X is a letter of the alphabet. Thus, your first source would be named 'srcA' , the second 'srcB', and so forth. This convention is used in this chapter.

The child atom of type kTrackModifierType indicates the type of the track being referenced. For a video track the type is VideoMediaType , for a sprite track it is SpriteMediaType , and so forth. Video tracks are the most common track type used as sources for effects. Only tracks that have a visible output, such as video and sprite tracks, can be used as sources for an effect. This means, for example, that sound tracks cannot be sources for an effect.

Figure 8 shows a completed input map that references two sources. The first source is a video track and is called 'srcA' . The second source, also a video track, is called 'srcB' .

You refer to a kTrackModifierInput atom by its index number, which is returned by the AddTrackReference function when you create the atom.

Figure 8 An example input map referencing two sources