【作者】 卢伟；

【导师】 魏洪涛；

【作者基本信息】 武汉理工大学 ， 通信与信息系统， 2008， 硕士

【摘要】 新一代视频压缩标准H.264/AVC支持从低带宽、高误码率的无线移动视频通信到高码率、低延迟的视频会议及在线流媒体等多种应用,在多媒体领域得到广泛关注和认同。相比于以前的标准,H.264能有效地提高编码器的压缩性能,但是标准的高复杂度也是目前视频应用的主要制约因素,所以研究标准在DSP(Digital Singnal Processor)上的实现及优化是非常有意义的。本文首先对H.264的核心技术进行分析研究,内容主要包括帧内/帧间预测、整数变换、量化、熵编码等,分析了它们的研究现状和在新标准中的创新点,在此基础上总结出了H.264/AVC未来的发展趋势。其次,研究了当前主要的两种帧内模式决策快速算法,一种是基于分组像素点的快速决策算法,该方法用分组像素点来代表一个块,在决策过程中每一个步骤中仅计算一组像素点的代价函数,以此减少计算点数,降低了复杂度;另一种算法是基于边缘方向直方图的快速决策算法,通过获得宏块的边缘方向信息,来确定预测模式的方向,从而获得最优或次优的帧内预测模式。本文从预测模式代价函数的选择和提前终止模式判决的基础上,提出了一种新的快速帧内预测模式算法,实验证明本文提出的算法与原算法相比,可以节约50%-75%左右的编码计算时间,信噪比平均下降0.03dB,码率有所上升。最后分析了TI公司的TMS320DM642芯片的系统结构,详细研究了H.264在DSP平台上的优化方法,所做的工作包括:调整存储空间的分配,改变存取的方式和变量的定义,采用内联函数,循环内部流水,线性汇编等方法对H.264中影响编码速度的瓶颈函数进行优化,结合DM642的两级Cache结构充分发挥DMA的能力等。通过优化前后实验结果的对比,可以看出基于DSP编码器的编码速度从之前的1.45帧/秒提高到8.35帧/秒,速度提高了6倍,取得了较好的优化结果。更多还原

【Abstract】 H.264/AVC video coding standard is designed to give a new technicial solution to a broad rang of applications, such as low-bit-rate conversational services and entertainment quality broadcast, interactive video-on-demand service etc. So this standard obtains much attention from academic and industrial fields. Compared with prior standards, H.264 has achieved great efficiency in compression of video, but the high-complexity of H.264 has always been a factor of restriction of application mostly, so to study the implement and optimization of H.264 based on DSP is significant.In this paper, the key technologies of H.264 are introduced first, such as intra/inter prediction, integer transform and quantization, entropy coding. We give a detailed analysis about the innovation and the research actuality mentioned above, sequentially the future about H.264.Secondly, the paper gives a detailed analysis about two arithmetics of fast intra prediction, the one is named as a sub-pixel rapid mode-decision algorithm, which uses a sub-pixel point instead of a block-pixel point. Every step in the mode-decision only to calculation a sub-pixel point to reduce the complexity of calculation; The other is based on the direction of the edge of the histogram rapid mode-decision algorithm, and counts the brink direction of the macroblock, determining the direction of forecasting models, in order to obtain the best or the second-best intra-prediction mode. Considering the cost function and the number of prediction models, the paper proposes a fast intra prediction algorithm. The results show that the new algorithm can reduce the coding time by 50% while the rate and PSNR change little.Lastly, the paper gives an introduction of structure of TMS320DM642 chips.Several key techniques concerning the porting of H.264 encoder from PC to DSP, such as the memory assignment, the modification of access mode and variable definition, inline assembly and application of pipeline, linear assembly, DMA based on two-level hierarchy cache, are adopted in the optimization procedures. The H.264 encoder on DSP is optimized to 8.35 frames per second encoding perfomace for CIF resolution video, compared to 1.45 frames per second before optimization.更多还原