Research And Development On The H.264 Rate Control Technology

H.264 video coding standard was developed jointly by ITU-T and ISO/IEC. H.264 encoder has an important part which is the rate control algorithm, whose function is to control the output bit quantity of the encoder. The rate control algorithm can adjust the encoder parameter to cause the encoding bit number adapting the band width change and the buffer capacity without appearing the frame jump situation. Simultaneously the code rate control section should be simple as far as possible in order to reduce encoder computation quantity, thus reduce the compression time and the delay time. At the same time, the simple rate control algorithm may reduce the time the bit stream stay at the encoder buffer, which can reduce the transmission delay and improve the transmission quality.Rate control algorithm is an indispensable part of coder, and it is one of important criterions to measure the advantage and disadvantage of coder. The continuous research and improvement of rate control algorithm has become an essential section, with broad use and rapid development of network technology, and in the case of extensive research and use of timely transmission technology and video compression algorithm. Thus, the research of rate control algorithm has the value of applications and important practical significance.In this paper, firstly the theory and significance of rate control is elaborated, the reasons and parameters that could cause the rate variance are discussed. Then the video coding standard and the key tools for H.264 are discussed, and the classic rate control algorithms and H.264 rate control algorithm are analysed, and the steps of H.264 rate control algorithm are analysed in detail. Lastly, the shortage of the classic rate control algorithms are associated with the existing research achievements of H.264 rate control algorithm, the direction to improve is pointed out, and a new rate control algorithm based on scene change has been put forward. According to the shortcoming of inaccurate target bit allocation for the scene change in JVT-G012, the concept of frame complexity is proposed to allocate the target bit; Utilizing the frame complexity to determine whether scene change occurs , and quantitative parameter is revised. Relevant software was also programmed by using C language under the JM10.2. The experimental results under the JM10.2 illustrate that compared with H.264 rate control algorithms, the newly proposed algorithm is capable of predicting the variance trend of video complexity more precisely and performing a more effective bit allocation. Consequently, the bit rate after encoding is closer to the objective one, the PSNR(Peak Signal-Noise Ratio) is also enhanced, and good visual quality is obtained, while paying small cost of algorithm complexity.