The MPEG-4 standard addresses the coded representation of both natural and synthetic (computer-generated) audio and visual objects. MPEG 4 Systems was developed to provide the necessary facilities for specifying how such objects can be composed together in a MPEG-4 terminal to form complete scenes, as well as how they should be multiplexed for transmission or storage. The term terminal is used here in a generic sense, and of course includes computer programs hosted on general purpose computers. The fundamental difference to MEG-1 and MPEG-2 systems is that MPEG-4 addresses the coded representation of audiovisual objects, both natural and synthetic. As a result, the Systems layer must address how these objects are composed together to form a scene (composition information or scene description), as well as how a user may interact with such objects. In addition, the object-based architecture necessitates changes in the way audiovisual information is multiplexed. In particular, it has a very flexible multiplexing structure and does not specify a transport layer facility as MPEG-2 did.