Research On The H.264 Rate Control Algorithm

H.264 as a new digital video coding standard is made by joint video team (JVT), and it is the main direction in video coding technique research in few years. In the video coding standard, the decoder norm describes syntax and semantics of the standard stream in detail, but gives no requirement to the encoder's strategy and algorithm. Just because of the difference between the encoder's strategy and algorithm, the performance of encoder is different, in which rate control plays an important role and is the key part of video coding technique.Rate control algorithm affects the quality of encoded picture and the output rate directly. It guarantees the reasonable bit allocation, controls the output rate of encoder and maintains to get higher quality of reconstructed image, by choosing different QP, frame skip, coding pattern.Firstly, the development and technical predominance of H.264 coding standard are introduced. Based on this, its frame configuration and inner technique are analysed. Its background and basic principles are discussed. Then, some classical rate control method and their principle are discussed.Then, the JVT-G012 rate control algorithm in the H.264 rate control proposal is mainly analysed. An improved rate control method is put forward based on JVT-G012. The main innovation is reflected in the following two aspects:(1) In frame level bit allocation's process, the H.264 rate control algorithm distributes averagely surplus number of bits of the GOP to the other un-coded-frames, and it has not considered the difference between the frames in the video sequence. This paper adopts the motion complexity to measure the movement activity of each frame, realizes frame level bit assignment according to the above method. And in the same way, an improved frame skip algorithm is proposed and implemented on JM8.6.(2) Because a linear model is usually used to predict the MAD and the QP quantization is the same in the JVT-G012, which costs too much operation and exists deviation, in the paper, an improved rate control algorithm for the basic-unit layer enconder is presented. Firstly, the MAD is predicted by a new time and space weighted model. Secondly, macroblock layer rate control strategy is used to distribute target bit. Finally, the quadratic R-Q model in the JVT-G012 is still adopted to calculate QP.Simulations show in standard test video sequence that this proposed algorithm can control the output rate, make the possession of the buffer much smoother, and it also can output bit stream more steadily. Meanwhile, the quality of video also has been improved accordingly.