Inside Macintosh: QuickTime Components
Some preview components only create a preview and rely on another component to display it. For example, by default, the movie preview component creates a picture preview for the file. This is displayed by the picture preview component.
Most preview components simply draw the preview. These are the simplest type of display components. They do not require any other event processing--including the scheduling of idle time--for example, to play a movie. The picture preview component is an example of this type of component.
Preview components that do not require a cache should have a subtype that matches the type of file for which they can display previews.
A preview component for sound would require event processing, since it would need time to play the sound. If your preview component requires event processing, you must have the pnotComponentWantsEvents flag set in its component flags field.
enum {
pnotComponentWantsEvents = 1,
};