H.264/AVC编码器的优化设计与实现

【作者】 闫冬；

【导师】 王建国；

【作者基本信息】 电子科技大学 ， 通信与信息系统， 2004， 硕士

【摘要】 近些年来移动通信和因特网技术得到迅猛发展,单一的语音和数据通信已不能满足人们的需求,而对于数字视频及图像传输业务的需求随之大幅度增加。另一方面,相比较其它类型的信息传输如文本和数据,视频通信需要占用更多的带宽资源,因此为了实现在带宽受限的条件下(如无线信道)的传输,视频源必须经过大量压缩。今天最为成功的视频压缩方案是混合编码器,其代表为基于H.263、MPEG-2等视频压缩标准的编码器。其中针对于低码率视频传输的H.263及其后续版本(H.263+、H.263++等)已被广泛应用于视频电话会议的解决方案中。但是作为早期的视频标准,其固有的缺陷也是明显的。由于技术上的局限性,在窄带条件下它无法保证视频内容的高质量传输和图像传输的连贯性。H.264/AVC是由国际电信联合会和国际标准化组织共同发展的下一代视频压缩标准。新标准中采用了众多的新的视频压缩技术:如以整数变换替代旧标准的DCT,采用去块效应滤波器改善图像主观质量,帧间预测采用更大范围的像素块(4×4～16×16)、像素精度更高的运动估计和多参考帧预测,应用多种帧内预测模式,基于上下文的变长编码或算术编码等。H.264/AVC仍然沿用的是传统的混合编码器结构,而在其实现策略中引入拉格朗日技术实现对编码器的率失真优化,使得编码器整体性能进一步提高。所有以上技术的应用使得H.264/AVC的压缩性能至少两倍于其它旧有视频压缩标准,能够实现更加广泛的视频应用,满足在低码率条件下进行视频的高质量传输要求。本文对H.264/AVC标准进行了较为系统的介绍包括编码器整体结构及各个模块基本算法的描述,这部分工作主要是通过详细阅读H.264/AVC最后草案的研究成果、分析相关文件及各模块算法的研究性文章得到的。同时对于影响编码器整体性能最大的运动估计及模式选择模块进行分析,讨论比较了多个搜索算法的性能并根据实际情况进行选择,引入拉格朗日算法通过大量实验统计得到且验证了算法参数将最后结果应用于对两个模块的优化,改善编码的率失真性能。最后,给出H.264/AVC编码器整体实现的解决方案,包括硬件平台及C语言实现的编码器结构、压缩流程。并针对视频会话的情况,选用一些图像内容类似的视频序列进行模拟测试,给出压缩效果和测试结论。更多还原

【Abstract】 With the rapid growth of mobile communications and Internat,voice and data communication cannot meet people’s need any more.The requirement for businesses of digital video and image is increasing enormously.On the other hand,video communications require very much bandwidth in comparison with other information types such as text and data.Thus to adapt with the bandwidth-limited channels,especially wireless channels,video source must be compressed extremely.The most successful class of today’s video compression schemes are called hybrid codecs,such as H.263,MPEG-2 etc.Codecs based on H.263 standard or its improved version H.263+ H.263++ have widely been adapted in the system of video telephony and conference.However,these early video compression standards have many drawbacks obviously just because of technology limitations.So those can’t afford the satisfied performance for high quality video transportation and low delay given the narrow bandwidth.H.264/AVC is the next generation video coding standard of ITU-T and ISO/IEC.Techniques the new standard uses include integer transform instead of DCT,the deblocking filter to enhance picture subjective quality,more types of block and more accurate motion compensation for inter prediction,more modes for intra prediction,and Context-Adaptive Entropy coding (CAVLC or CABAC) and so on.In terms of coding efficiency,the new standard is expected to provide at least 2x compression improvement over previous standards.This thesis gives an overview of H.264/AVC standard and basic algorithms in every part of encoder.These parts,which have a heavy influence on the performance of the encoder,motion compensaton and mode decision,are discussed and analysed through plenty of experiments.At the same time,the lagrangian algorithm is introduced to optimize the encoder operation so as to increase the rate-distortion performance of it. Finally, an implementation of the encoder should be given including hardware platform and software flow chart,and its test result and conclusion.更多还原