MPEG-4 is a standardization effort under the auspices of ISO being developed by MPEG (Moving Picture Experts Group), the committee that also developed the Emmy Award-winning standards known as MPEG-1 and MPEG-2 MPEG-4 addresses the "generic coding of audio-visual objects." In contrast to all other existing audio or video representation standards, MPEG-4 adopts an object-based approach for content description: the content is assumed to be constructed out of individual and independent entities called objects, which are coded and transmitted separately. These objects include, for example, rectangular or arbitrarily shaped natural video, graphics, text, natural or synthetic audio, and even face or body animations. MPEG-4 has defined a number of representation tools to address the coding needs of a large variety of media. Coding of such objects, however, is only the first step into constructing a complete multimedia scene. Additional information is needed in order to: 1) describe how these objects should be placed in space and time, 2) how they may interact with each other and the end-user, 3) how to multiplex all this information into one or more streams for delivery over a variety of networks, and 4) ensure proper synchronization among the various streams. This information is the realm of the MPEG-4 Systems specification (Part 1 of the MPEG-4 standard), which is also responsible for the overall architectural definition of MPEG-4. We describe the key features of the MPEG-4 Systems (ISO 14496-1) specification and their encoding methodology: scene description and BIFS, animation streams, object descriptors, the sync layer, object content information, as well as multiplexing. We also describe currently available products using MPEG-4, as wall as early product prototypes still in the development stage.
