Large Scale Video Conferencing A Digital Amphitheater.pdf

Large Scale Video Conferencing: A Digital Amphitheater Ladan Gharai Colin Perkins Ron Riley Allison Mankin USC Information Sciences Institute March 1, 2002 Abstract In this paper we address the problem of large-scale video conferencing, both from a systems and user inter- face point of view. We present the architecture and current implementation of our video conferencing tool, the Digital Amphitheater, which facilitates large scale video conferencing for hundreds of participants in a natural and cohesive environment. We describe a unique user interface that aims to engender a feeling of presence, using background substitution, eliminating control functions from the screen, and allowing participants to view themselves in an amphitheater setting. 1 Introduction Video conferencing, once a novel technology, has become a staple of modern business. It is increasing common to conduct small meetings via video conferencing, saving time and economizing on travel budgets. A variety of conferencing systems are available: commercial products tend to derive from the H.323 standards [18] and support point-to-point conferencing only, or multipoint conferencing based around a single central server. 1 Open source systems such as vic [13] and rat [7] are examples of the alternative light-weight sessions model [8], which rely on IP multicast and relaxed membership controls to scale to very large sessions. Our experience with the implementation of systems based on the light-weight sessions model has led us to realize that, whilst they provide significant advantages in scaling compared to H.323 based systems, there are many aspects to the problem of video conferencing with hundreds of participants which are left unsolved. The first and most obvious is the user interface: how to fit a large number of participants onto a single screen, in a cohesive and visually comprehendible manner? For example, assuming a screen size of 1024x1024 pixels, upto 35 QCIF (176x144 pixel) video streams can be