Handling audio and video streams in a distributed environment

Handling audio and video in a digital environment requires timely delivery of data. This paper describes the principles adopted in the design of the Pandora networked multi-media system. They attempt to give the user the best possible service while dealing with error and overload conditions.Pandora uses a sub-system to handle the multi-media peripherals. It uses transputers and associated Occam code to implement the time critical functions. Stream implementation is based on self-contained segments of data containing information for delivery, synchronisation and error recovery. Decoupling buffers are used to allow concurrent operation of multiple processing elements. Clawback buffers are used to resynchronise streams at their destinations with minimum latency.The system has proved robust in normal use, under overload, and in the presence of errors. It has been in use for a number of years.The principles involved in this design are now being used in the development of two complementary systems. One approach explodes Pandora by having the camera, microphone, speaker and display as independent units linked only by the LAN. The other approach integrates these devices as peripheral cards in a powerful workstation.