Co-ordinating stored media

It is now technically possible to construct distributed systems which support audio and video information. These media are inherently time dependent and so their use in combination requires suitable techniques for synchronizing a variety of presentation streams to be available. The steps involved in the capture or retrieval and in the encoding and transmission of these media may take significant periods of time. Audio interfaces often buffer one or two seconds of data to ensure smooth reproduction despite unpredictable operating system scheduling of the processes and disc transfers involved; video compression and decompression can be a time consuming process, even when performed by specialized hardware. The consequence of these real time delays is that the system designer must take a flexible approach to synchronization, and must consider the positioning of the associated control functions carefully. There is a need for a suitable abstract model of the various media which can express synchronization mechanisms in a way which is independent of the details of the particular media involved. The author presents a model of a continuous medium