A coded-domain video combiner for multipoint continuous presence video conferencing

This paper presents a coded-domain combining technique which can accommodate up to six users for continuous presence multipoint video conferencing. This technique is based on a group-of-block (GOB) video unit in the H.261 video standard. Three important technical issues including frame rate synchronization, combiner delay accumulation, and potential quality degradation at the GOB boundary, are addressed. A frame rate synchronization scheme is proposed for the coded-domain combiner. It is observed that delay accumulation will not occur at the combiner with the proposed multiplexing strategy. Further, simulation results indicate that the output perceptual quality is very comparable even without special motion search handling at the GOB boundary. This implies that the proposed scheme can be applied to standard terminals. Finally, we demonstrate the viability of this software-based coded-domain combiner for continuous-presence multipoint video conferencing with a fully functional experimental prototype built around a low-cost personal computer.