A study of MPEG-4 rate control scheme and its improvements

This paper discusses some practical issues in implementing the MPEG-4 Q2 rate-control scheme, and proposes a number of ways to improve it. The improved algorithm has the following main features: 1) the bits allocated to each P-frame or B-frame are in proportion to its distance from the end this GOP. i.e., more bits are allocated to the frames that are nearer to their reference I-frame; 2) the target buffer level is a function of the frame position in the GOP, so that it will be achieved gracefully at the end of a GOP; and 3) the quantization value of an I-frame is decided based on its spatial complexity. Experimental results show that the improved rate-control scheme has significantly reduced the occurrence of frame skipping, increased the average PSNR by up to 0.6 dB, and improved the perceptual quality of the reconstructed video.