【作者】 刘敏；

【导师】 魏志强； 孟庆春；

【作者基本信息】 中国海洋大学 ， 海洋信息探测与处理， 2007， 博士

【摘要】 多媒体通信将是新一代通信系统的典型业务和显著特征,而视频编码技术是多媒体技术的基础和核心。AVS-M标准是中国最近自主制定的数字音视频编码编码系列标准(AVS)中的第七部分:移动视频编码标准,可广泛应用于交互存储媒体、宽带视频业务、多媒体邮件、远程视频监控、视频会议、可视电话等多个领域,是我国面向下一代移动通信的视频编码标准。AVS-M标准仍基于以前视频编码标准的运动补偿混合编码方案,为了实现更高的编码效率,AVS-M标准采用了许多新的编码技术,如新型帧内预测、多尺寸编码块模式、多参考帧预测、1/4像素精度运动矢量、整数变换量化、去方块效应滤波器等。这些新特征使AVS-M标准能够提供与最新的国际视频编码标准H.264/AVC相当的编码效率,另一方面,这些新技术的采用极大地增加了AVS-M编解码器的计算复杂度,因此实时编解码器的实现面临巨大的挑战,需要寻找高效的优化算法,以减少巨大的计算量。本文从实时视频应用的角度,对AVS-M编码过程中的帧内预测、帧间预测、运动估计、变换量化等方面进行了研究。具体研究内容包括:1、针对帧内预测编码的复杂性,本文提出一种基于方向信息和时空相关性的帧内预测模式选择快速算法。该算法利用当前宏块内的边缘方向信息和帧内预测模式的时间、空间相关性,以率失真优化(RDO)为判决依据,快速进行帧内模式选择。2、针对帧间编码模式的复杂性,本文提出一种快速模式选择算法。该算法基于对最佳模式选择结果的统计分析,将全部编码模式进行分类,对SKIP模式采用提前终止判决,而对其他模式通过判别宏块的一致性和比较宏块的空时相关性逐类型比较,可有效减少待选择的模式数量。3、针对AVS-M编码器中计算量最大的运动估计模块,本文从整数像素运动矢量搜索和分数像素运动矢量搜索两个方面分别进行了讨论和改进。整数像素运动矢量搜索过程中,提出了一种基于起点预测和早停止的自适应快速运动估计算法,该算法通过统计和分析当前块的相关矢量,预测运动估计的初始搜索起点,结合有效的搜索路径和中止准则,可以有效的实现整数像素最优运动矢量搜索过程中速度与效果的折中。针对AVS-M分数像素运动矢量搜索的复杂性,提出了一种基于预测的快速分数像素运动矢量搜索算法代替全搜索算法,大幅度地减少了搜索点数量和达到较好的匹配效果。4、全零块检测是面向低比特率的视频编码器常用优化方法之一,根据AVS-M视频编码标准整数变换的新特点,对其中的全零块检测阈值进行了推导,提出一种基于全零块检测的运动搜索提前终止准则。针对AVS-M的多编码模式,进一步将全零块检测用于AVS-M中多种编码模式的选择,在保持AVS-M编码器编码性能的同时,显著提高了编码器的编码速度。本文在最后一章对全文进行了总结,并且对今后进一步的研究方向进行了展望。更多还原

【Abstract】 With the emergence of communication networks, along with the rapid growth of multimedia service, the role played by multimedia communication has become increasingly important and essential in next generation communication system. Therein, video coding is the fundamental and kernel technique in emerging multimedia/video communication. AVS-M is the latest video coding standard developed by China for mobile application, which is the part 7 of domestic AVS (Audio Video coding Standard) series standard. AVS-M is designed to give a technical solution for a broad range of applications, such as interactive storage media, broadband video service, multi-media mail, long distance video surveillance, video conference, and video phone, etc. It is the video coding standard orienting next generation mobile communication in China.The design of AVS-M is based on conventional block-based motion-compensation hybrid video coding concepts. For the enhancement of the coding efficiency, AVS-M adopts new tools as followed: new intra frame prediction, variable block-size with seven block sizes in motion prediction, multiple reference picture, quarter-pixel accuracy for motion vectors, integer transform and loop deblocking filter. With these features, AVS-M can provide improved performance close to the newest international video coding standard H.264/AVC. At the same time, the complexity of the AVS-M codec is increased remarkably. Accordingly, the real-time video codec demands higher-powered processor and faster-speed algorithms. So the main endeavor of this paper is to achieve maximal processing speed and better video compression quality through optimization for intra prediction, inter prediction, motion estimation, integer transform in the AVS-M encoding process. The major works of the thesis are as follows.1. To reduce the complexity of intra prediction, a fast intra prediction mode selection algorithm is proposed. It uses the information of edge direction in the current coding macroblock and spatio-temporal correlation of intra prediction modes to fast determine the best mode with the RDO (Rate Distortion Optimization) criterion.2. To reduce the complexity of inter prediction, a fast inter prediction mode decision algorithm is proposed. It classifies all modes by both homogeneity and spatio-temporal correlation of macroblock based on the statistic analysis of the results of the optimal modes. The SKIP mode can be early terminated and other modes can be compared type by type. So the number of calculated modes can be decreased efficiently.3. As the most important module in the AVS-M encoder, motion estimation is accelerated in two perspectives. In the process of integer pixel motion vector search, by calculating and analyzing the relevant motion vectors of current block, an adaptive fast motion estimation algorithm is proposed. The algorithm can effectively reduce computation in the optimal integer pixel motion vector search process by some effective techniques, which are composed of the prediction of initial search point, half-stop criteria and adaptive search modes. Meanwhile the algorithm can maintain comparable search quality. To reduce the complexity of fractional pixel motion estimation, a prediction based fractional pixel motion estimation algorithm is proposed to replace the full search algorithm. It can efficiently decrease the number of search points and come to a good matching.4. For most sequences at middle or low bit rates, the values of prediction residuals usually are very little, and most of them will be reduced to zero after transformation and quantization. All-zero block detection is one of the common optimization methods in low bit rate video coding. According to the new characteristics of AVS-M standard, the threshold for all-zero block detection is derived and an advanced stop principle of motion estimation based on all-zero block detection is proposed. In accordance with the feature of multiple encoding modes, all-zero block detection is applied to the AVS-M mode selection, and further improves the efficiency of motion estimation. Experimental results show that the proposed algorithm can reduce encoder complexity significantly while maintaining PSNR and bit rate almost unchanged.The conclusions and directions for future research work are discussed in the last chapter of this thesis.更多还原