Study Of Rate Control Algorithm For Video Coding

Rate control algorithm is one of the key techniques for video coding. It will affect the bandwidth of encoded bits and reconstruct image quality directly. Because the complexity and motility of images are not same, it will lead to the output bits huge change. It is necessary that the change is controlled to a limited range by some rate control algorithms.In this paper, the international standards and many kinds of rate control algorithms are studied firstly, and their advantages and disadvantages are analyzed. Considering the shortages of VM8 and zero coefficient percentage algorithms, two improved rate controlling algorithms are presented.For the old VM8 algorithm, the target bits are allocated according the buffer and the remainder bits of this GOP. The difference of images is not considered. This will lead to warp of target bits. The improved algorithm of VM8 allocates bits for every frame according to static MAD and dynamic MAD of Video sequences. So the complexity of every image is considered fully. This way is more logical and can get better results. Beside that, an improved algorithm of Zero Coefficient percentage is proposed in this paper. For the new algorithm, the old way of measurement about image complexity MAD is obsolesced and the new one, zero coefficient percentage, is adopted. When allocating the target bits for the encoding frame, the Zero Coefficient percentage is a good factor and is more effective than Mean Absolute Difference. The new algorithm adopts some advantages of VM8 and Zero coefficient percentage algorithms. It can control the bits more accurately.Experimental results show that the improved algorithms can alleviate the buffer's fluctuating rang and avoid frame skipping effectively. In addition, the decoded pictures' PSNR are also increased.