MPEG-4, under the auspices of the ISO, is specifying tools to enable object-based audio-visual presentations. These include tools to encode individual objects, compose presentations with objects, store these object-based presentations and access these presentations in a distributed manner over networks. The main distinguishing feature of object-based audio-visual presentations is the scene composition at the user terminal. The objects that are part of a scene are composed and displayed at the user end as opposed to encoding the composed scenes as is done in the case of MPEG-2. Such object-based representation and presentation has several benefits including compression efficiency and interaction with individual objects.

We describe the implementation of a streaming client-server system for object-based audio-visual presentations in general and MPEG-4 content in particular. The system augments the MPEG-4 demonstration software implementation(IM1) for PC's by adding network-based operation with full support for the Delivery Multimedia Integration Framework (DMIF) specification, a streaming PC-based server with DMIF support (via Xbind Inc's XDMIF suite), and multiplexing software. We describe XDMIF, the first reference implementation of the DMIF specification. The MPEG-4 server is designed for delivering object-based audio-visual presentation. We discuss the issues in the design and implementation of MPEG-4 servers. The system also implements a novel architecture for client-server interaction in object-based audio-visual presentations, using the mechanism of command routes and command descriptors. This new concept of command routes and command descriptors is useful in developing sophisticated interactive applications.