A CODED-DOMAIN VIDEO COMBINER FOR MULTIPOINT CONTINUOUS PRESENCE VIDEO CONFERENCING

This paper presents a coded-domain combining technique which can accom modate up to six users for continuous-presence multipoint video confer encing. This technique is based on a group-of-block (GOB) video unit i n the H.261 video standard. Three important technical issues including frame rate synchronization, combiner delay accumulation, and potentia l 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 wit h the proposed multiplexing strategy. Further, simulation results indi cate that the output perceptual quality is very comparable even withou t special motion search handling at the GOB boundary. This implies tha t the proposed scheme can be applied to standard terminals. Finally, w e demonstrate the viability of this software-based coded-domain combin er for continuous-presence multipoint video conferencing with a fully functional experimental prototype built around a low-cost personal com puter.