Dynamic rate control in multipoint video transcoding

This paper presents a dynamic rate control method for video transcoding to enhance the visual quality of the participants and regions of interest in multipoint video conferencing. This method 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 by using a rate-distortion optimized bit allocation approach. The simulation results show that the visual quality of the active sub-windows is significantly improved with the cost of degrading the temporal resolution of the inactive sub-windows which is relatively invisible to human perception. In addition, we also propose a dynamic distortion weighting adjustment based on H.263 TMN-8 framework to improve the quality of the regions of interest such as the face regions, since the face regions are usually the main focuses in video conferencing. The quality of face regions can be effectively enhanced at most frames in our simulation results. The computational complexity of the proposed algorithm is pretty low thus makes it well suited for real-time applications.