Abstract
A multipoint video conferencing system employs a transcoder with a dynamic sub-window skipping technique to enhance the visual quality of the participants of interest. The system firstly identifies the active conferees from the multiple incoming video streams by calculating the temporal and the spatial activities of the conferee sub-windows. The sub-windows of inactive participants are dropped and the saved bits are reallocated to the active sub-windows. Numerous motion vector composition schemes can be used to compose the unavailable motion vectors in the dropped frames due to limited bit-rates or frame-rates of the user clients in video transcoding. The present invention employs a pre-filtered activity-based forward dominant vector selection (PA-FDVS) scheme which provides accurate approximation of motion vectors with low computational cost and memory requirement. Simulation results show the visual quality of the active sub-windows is significantly improved at the cost of degrading the temporal resolution of the inactive sub-windows, which degradation is relatively invisible to human perception.