Inside Macintosh: QuickTime Reference

Movie Media Handler Tasks

The Movie Media Handler's primary task is to make each embedded movie appear like a single, integrated element within its containing movie.

This means that it must mediate between the requests made by its containing movie and the capabilities of the embedded movie. These requests are typically made in the form of some kind of "set property" call to the Movie Media Handler. The properties themselves can be divided into a few groups: spatial, audio, and temporal with a few miscellaneous additions. Because the "right" behavior varies from case to case, the Movie Media Handler allows the exact behavior to be specified within each movie media sample.

To allow for composition to occur within the embedded movie as intended, in this case, the embedded movie's tracks are composed together independently of the containing movie, and then the transfer mode of the containing track is used to compose the result into the final containing movie's composition. If the transfer mode is attached, the behavior is quite different. The transfer mode of the containing track is applied to each track within the embedded movie. The tracks are drawn directly into the containing movie's composition buffer, allowing their transfer modes to interact with any background provided by the embedded movie. This effectively destroys the original transfer mode information, and so this mode is generally useful for embedded media streams that only contain a single visual track, such as still images. The SMIL importer only slaves transfer modes when a particular transfer mode is requested in the SMIL composition. Support for transfer modes is a QuickTime-specific extension to SMIL to allow for the application of the transparency information stored in GIF and PNG images.

Inside Macintosh: QuickTime Reference