Dynamic region of interest transcoding for multipoint video conferencing

This paper presents a region of interest transcoding scheme for multipoint video conferencing to enhance the visual quality. In a multipoint video conference, usually there are only one or two active conferees at one time which are the regions of interest to the other conferees involved. We propose a Dynamic Sub-Window Skipping (DSWS) scheme to firstly identify the active participants from the multiple incoming encoded video streams by calculating the motion activity of each sub-window, and then dynamically reduce the frame-rates of the motion inactive participants by skipping these less-important sub-windows. The bits saved from the skipping operation are reallocated to the active sub-windows to enhance the regions of interest. We also propose a lowcomplexity scheme to compose as well as trace the unavailable motion vectors with a good accuracy in the dropped inactive sub-windows after performing the sub-window skipping. Simulation results show that the proposed methods not only significantly improve the visual quality on the active sub-windows without introducing serious visual quality degradation in the inactive ones, but also reduce the computational complexity and avoid whole-frame skipping. Moreover, the proposed algorithm is fully compatible with the H.263 video coding standard. Keywords-video coding, video transcoding, bit-rate control, multipoint control unit (MCU), video conference. 1 Corresponding author