Research For The Ratio Control Algorithm In H.264

Rate control serves as an important technique to moderate the bit rate of video transmission over a channel of limited bandwidth and to control the bit allocations within a video sequence to maximize its overall visual quality. H.264/AVC is the latest video coding standard and it reflects the latest advances of video coding techniques aiming to addresses a broad variety of applications, ranging from wired/wireless conversational, broadcast, and interactive multimedia applications for a wide range of bit rates. The output bit rate and video quality of a video encoder depend on several coding parameters such as the quantization parameter and coding mode. In particular, choosing a large quantization parameter reduces the resulting bit rate, while at the same time reducing the visual quality of the encoded video. Since the level of redundancy changes from frame to frame, the output bit rate is inherently variable. A rate control scheme then must be employed during the video compression process to adjust coding parameter settings to prevent visual artifacts such as blurring, blocking, and jitter. So the encoded video quality could consistently be kept at the highest possible quality level for each frame and within each frame. The goal of rate control, therefore, is to keep the output bit rate within constrained limits and achieve maximally uniform video quality. This goal can be achieved by optimal bit allocation and accurate quantization parameter determination. To be more specific, the bit allocation scheme is employed to distribute the bit budget among coding unites such as frames, or macroblocks in such a way that the overall distortion is minimized. The accurate quantization parameter for the encoder is then determined to meet the bit budget.In this paper, the basic theories for video encoding and the development of video encoding standard are introduced first, and in Chapter 2 I introduce the aim of the rate control algorithm and the effect factors of the bit rate ,then the R-D model which is the important technique of the rate control and a few typical methods of rate control are analyzed.In Chapter 3, the main parts of H.264 are introduced first ,and then I introduce the rate control algorithm of H.264/AVC, which are the theories basis of the new arithmetic. In order to improve the demerit, I propose a new rate control algorithm in frame level for H.264/AVC using the Cauchy-Density-Based R-D model and the occupancy of the buffer. Simulation results show that our proposed algorithm achieves a better performance on veracity and image quality.In Chapter 4, in order to reduce the demerit that costs too many operations and exists deviation of the traditional linear model, I present a new weighted mode to predict the MAD. Then I propose a new rate control algorithm in macroblock level for H.264/AVC. achieving a better performance on veracity.In Chapter 5, a brief summery and prospect is given.