基于H.264/AVC的码率控制算法研究

【作者】 吴东伟；

【导师】 樊养余；

【作者基本信息】 西北工业大学 ， 信号与信息处理， 2007， 硕士

【摘要】 H.264／AVC是由JVT(Joint Video Team)共同制定的新一代视频压缩标准。它能在较低的带宽下传输高质量的图像，而且对基于IP的视频应用和无线网络具有更“友好”的支持。但是，由于其编码器的高复杂度和混合编码的局限性，导致它很难在窄带宽下保持图像质量的连贯性。同时，H.264标准中只规定了视频码流的语法和解码的方法，没有对码率控制给出明确的定义，这就为码率控制的研究提供了广阔的空间。 本文从视频应用的角度，针对H.264的编码器复杂度和码率控制方面的算法进行了研究和分析。 论文首先针对H.264的编码体系结构和关键技术进行了研究，在分析国内外研究现状的基础上，指出了算法的缺陷和改进方向。其次，在H.264标准代码这一测试软件平台上对H.264的关键技术带来的增益和复杂度进行比较，并对代码深入分析，提出代码精简的建议。最后，论述了码率控制的原理和意义，对码率控制技术在不同的视频压缩标准中的发展进行分析，并提出两点改进措施：针对JVT-G012算法中量化参数初始化不合理会造成整个序列的码率和压缩质量不平稳的缺点，提出一种自适应初始化量化参数的方法。实验表明，改进后的算法能很好地保证码率和PSNR(Peak Signal to Noise Ratio)的平稳性；现有码率控制算法多采用简单但不符合人眼视觉特性的MAD(mean absolute differences)作为衡量编码失真的依据，本文采用基于模糊积分的图像失真度量代替MAD，提出一种基于宏块条的自适应码率控制算法，实验结果表明，所提出的方法无论是在CBR(Constant Bit Rate)还是VBR(Variable Bit Rate)下，码率控制都相当准确，并且能获得较高的PSNR和良好的主观视觉效果。更多还原

【Abstract】 H.264/AVC is a video coding standard of new generation proposed formally by JVT(Joint Video Team).As the latest standard in video codec field,H.264 has such advantage as high compression rate, friendliness to IP and wireless network. It can’t assure the consistency of video quality under low bandwidth because of the high complexity and the drawbacks of mixed coding.H.264 standard only prescribes video coding bit stream syntax and the method of decoding but has no definition about rate control. It provides more wider space for searching.Several issues for real-time video coding such as the arithmetics of rate control and the codec complexity will be addressed in this paper.Firstly the codec and the key tools for H.264 are discussed .We give a detailed analysis about the research actuality and the shortage of different techniques, and point out the direction to improve.Then we give some advices about the condensing of the standard code based on the comparation of the plus and complexity brought by all kinds of tools adopted by H.264. Lastly, the mechanism and development of rate control in different standards are described. The arithmetic employed by JVT-G012 has a problem that for different preliminary quantization parameters JM achieves insecure rate and PSNR(Peak Signal to Noise Ratio),so an adaptive method for confirming the preliminary quantization parameters is proposed. The test results denote that the improved arithmetic plays good in rate and PSNR. The usual rate control arithmetics of H.264/AVC employed MAD (Mean Absolute Differences) which is simple but doesn’t comply with the human visual system as the measurement of the coding error. In this paper, we use the image distortion metric based on fuzzy integral, and apply it to the rate controlling. The result shows this arithmetic achieves both higher PSNR and higher subjective visual quality, no matter under the CBR (Constant Bit Rate)case or VBR(Variable Bit Rate) case.更多还原