【作者】 周小兵；

【导师】 王占杰；

【作者基本信息】 大连理工大学 ， 计算机软件与理论， 2006， 硕士

【摘要】 近年来,随着宽带网络的普及和多媒体技术的不断发展,人们对数字视频业务产生了越来越浓厚的兴趣。视频会议系统、视频监视系统、远程教育、视频点播系统(VOD)、高清晰数字电视(HDTV)以及网络聊天软件等多媒体实时业务逐渐得到广泛的应用。尽管网络状况在改善,但是相对于快速增长的视频业务而言,网络带宽资源仍然是远远不够的。在这种情况下,研究具有高压缩比、高质量的视频编码技术成为当前多媒体领域的热点问题。 新一代数字视频编码标准H.264,采用了多模式的帧间预测、1/4像素精度的运动估计、基于4×4块的整数变换等关键技术,使得编码性能得到大幅度的提高。实验证明,在相近的主观质量下H.264编码器要比基于H.263标准的编码器减少50%左右的码率。但是,在编码性能提高的同时,算法复杂度也大大增加了。这导致了H.264参考软件编码速率非常的低。因此,必须对H.264编码器进行编码速率的提高之后,才能应用于多媒体实时通信中。本文对H.264视频编码标准进行深入的研究,重点分析造成编码速率瓶颈的原因,并在此基础上研究提高编码速率的方法,包括帧内预测模式的快速选择、帧间预测模式的快速选择以及快速运动估计的应用三方面。实验结果表明本文实现的编码器同H.264参考软件相比,在PSNR值和压缩比降低较小的情况下,有效的提高了编码速率,达到视频实时通信的要求。本文同时还将实现的编码器同基于H.263标准的编码器进行对比。对比结果表明,本文实现的编码器在保证了主观质量的同时,降低了约40%-50%的码率。 在实现的H.264编解码器的基础上,本文同时实现了一个局域网内的音视频通信软件AVChat。该软件在局域网之内实现点对点的音频和视频的实时通信。测试结果表明,本文所实现的H.264编解码器在该软件中运行良好,在使用较低视频码率的情况下能达到较高的视频主观质量。本文所实现的音视频通信软件,扩展后可应用于视频会议、远程教育等系统之中。更多还原

【Abstract】 In recent years, with the prevalence of broadband, and with the development of multimedia processing technology, digital video service has gained people’s attention greatly. Realtime multimedia applications, such as videoconference systems video monitor systems HDTV etc., have been widely used. Although network environment has been progressing a lot, the bandwidth resource is still limited as far as the fast growth of multimedia applications is concerned. Therefore, video coding technologies that can produce high compression ratio and high picture quality have been a hot spot issue in multimedia field.The H.264 is the newest international video-coding standard established and released by the ITU-T and ISO/IEC together. A number of new features have been applied to the new standard, including multi-block inter prediction, 1/4 fractional pixel motion estimation, 4x4 block integer transform, CABAC etc., and therefore it has enhanced compression performance. Experimental result reveals that the bit rate reduces about 50% under the same visual quality, compared with the former video-coding standard H.263. However, the algorith complexity increases greatly at the same time, so it needs be optimized when applied in multimedia communication systems. This Paper studies the H.264 standard in detail, analyze the bottleneck of the coding speed, and implement an optimized codec. Experimental result reveals that, compared with the reference codec, the PSNR and compression ratio of the optimized codec fall off slightly, while the coding velocity advances greatly, and afford satisfaction to realtime multimedia applications’ needs.Based on the implemented H.264 codec, this paper also implements an audio-video communication software AVChat in LAN. AVChat provides point to point audio and video communications in realtime. Experimental result shows that the H.264 codec implemented in this paper works smoothly in AVChat. It performs a good video quality while costs a low bit rate. AVChat can be expanded, and put to use of realtime multimedia applications such as videoconference systems, etc.更多还原