QuickTime 4 Reference

Movie Playback

During data retrieval, such as playback of a movie, a media handler component isolates your application and the Movie Toolbox from the details of how to retrieve data from a particular storage medium. Therefore, unless you are writing your own media handler, you do not have to directly use data handler components in your application; the retrieval of your data will be taken care of for you by the media handler the Movie Toolbox calls. However, you can call the data handler directly if you need to explicitly tell the data handler something, such as to use less memory when caching QuickTime data. If you are reading from a non-Macintosh storage medium, or multiple storage media, you might need to write your own data handler.