MPEG Video Transcoding with Joint Temporal-Spatial Rate Control

Abstract

Novel temporal-spatial rate control solutions for MPEG video transcoding are investigated in this paper. We present two rate control approaches for MPEG video transcoding, one for IPP (including only I and P frames, no B frames) streams and the other for IBP (including I, P and B frames) streams. The proposed rate control schemes adapt the frame rate and the quantization step size simultaneously according to the available channel bandwidth to achieve a good temporal-spatial quality tradeoff. In our proposed solutions, key frames are not allowed for skipping in order to maintain the prediction sequential order, and the MPEG-4 quadratic Rate-Qtz model is adopted to calculate the quantization step size from a given target bit rate. Simulations show that the proposed rate control method for IPP stream transcoding achieves a higher average PSNR value than the MPEG-4 rate control (frame level) with a constant frame rate in CBR channels. Furthermore, the proposed rate control method for IBP stream transcoding can significantly enhance the transcoded video quality in VBR channels, in comparison with straightforward MPEG video transcoding by adjusting the quantization step size at a constant frame rate. The two proposed transcoders are in low computational complexity so that they can be used in real-time transcoding applications.