Constant-Quality CBR Rate-Control Algorithms for MPEG-4 Video Transcoding

Two constant quality (CQ) CBR algorithms for MPEG-4 video transcoding (FLCQT and MVCQT) are proposed in this paper. These algorithms are developed based on the CQ CBR encoding algorithms. A new Laplacian rate/distortion model is developed to predict the transcoder output quality relative to the original. This model is then used by the proposed rate control algorithms to determine the frame QP (for FLCQT) or macroblock QPs (for MVCQT). Simulation results suggest that the proposed transcoding algorithms generally give a lower quality variation with similar average PSNR and lower bitrate than the reference encoding and transcoding algorithms. Like Cheng-Yu Pai et. al., (2006), an extra degree of freedom is offered so that one can trade between lower PSNR variance and higher average PSNR.