摘要
H.264是由ISO(国际标准化组织)与ITU(国际电信标准化部门)为了获得更好的压缩和传输性能而联合制定的新一代视频编码标准。H.264引入了当前视频编码的新技术,包括多种宏块大小模式、4×4整数变换、帧内预测、去块效应滤波、统一的熵编码等。与现有的其它视频编码标准相比,这些新技术使得H.264在相同的情况下可以得到更高的压缩比和更好的图像质量,这就使它具有很好的应用前景。随着嵌入式系统的广泛应用,在嵌入式系统中实现视频的编解码已经成为H.264研究的重点和难点之一。本文在详细分析了H.264编码原理的基础上,研究了复杂度很高的运动估计和模式选择的相关算法,然后在嵌入式平台PXA255上面实现基于H.264的实时视频采集编码系统。
首先,在熟悉视频编码相关理论的前提下,介绍了H.264编码器结构和档次划分,并且详细分析了H.264使用的关键技术以及H.264的编码性能。从主观和客观两个方面比较了H.264与MPEG2、MPEG4和H.263的编码性能,从测试的结果可以看出不论从主观还是客观方面H.264都具有更好的编码性能。
其次,详细分析了运动估计中的搜索算法,并且比较了几种搜索算法的性能。实验结果显示,全搜索具有最好的搜索性能,但是搜索的复杂度很高,不适合在实际中应用。而三步搜索、菱形搜索、六边形搜索算法和混合的非对称多六边形搜索算法等快速算法在不严重改变搜索性能的情况下可以很大程度提高搜索速度。
再次,重点研究了基于Lagrangian率失真优化算法的模式选择,并对率失真优化算法进行相应的改进,以提高模式选择的速度。实验结果显示,改进后的模式选择算法可以很大程度的节约时间,而且不会对编码性能有大的影响。
最后,将H.264编码算法应用在嵌入式平台PXA255上实现基于嵌入式linux的视频采集编码系统。将H.264编码软件X264移植到PXA255上,实现对采集到的视频进行压缩,并且对编码软件进行优化。实验结果表明,优化后的编码软件基本可以对采集到的视频进行实时编码。
ISO(International Organization for Standardization) and ITU(International Telecommunication Union) work together to work out a new video coding standard-H.264,in order to obtain better compression and transmission performance.The H.264 standard introduction the new technologies of current video encoding,including multi-slice size model, 4×4 integral transformation, intra prediction, the effect of filtering to block, entropy coding of the reunification and so on.Compared with other video coding standard of existing,the new technology allows H.264 coding standard can get a higher compression ratio and better image quality in the same circumstances. So,it has good application prospect.With a broad application of embedded systems, Implementation the video codec in the embedded systems has become the focus and difficult one of H.264 study.In this paper, on the basis of detailed analysis of H.264 coding theory,study the campaign estimates and choose the mode of algorithms of a high degree of complexity , and then accomplishment real-time video capture encoding system based on H.264 in the PXA255 of embedded platform.
Firstly,Under familiar the theory of video encoding premise, introduce the structure and level of the H.264 encoder,and multianalysis the key technology and encoding performance of H.264. Comparison of H.264、MPEG2、MPEG4 and H.263 encoding performance from two aspects of subjective and objective.From the test results, H.264 has better coding performance both the aspect of subjective or objective.
Secondly,detailed analysis of search algorithm of the motion estimation,and compared the performance of several search algorithm. The results show that the whole search has the best search performance, but a high degree of complexity.So,not suitable for application in practice.But,The fast algorithm of three-step search、diamond Search、hexagonal search algorithm and mixed asymmetrical multi-hexagonal search algorithm can greatly improve search speed Without a serious change in search performance.
Thirdly,emphatic study mode selection of rate distortion optimization algorithm based on Lagrangian,and increase speed of mode selection by improvement the rate distortion optimization algorithm.The results show that the improved model algorithm can save time large degree,moreover without impact the coding performance major.
Finally, H.264 encoding algorithmapplication on PXA255 of embedded platform to accomplishment real-time video capture encoding system based on embedded linux. X264 of H.264 encoding software will be transplanted to PXA255 to achieve the collection of video compression,and optimize the encoding software.Experimental results show that the encoding software of optimization can accomplishment of the basic real-time video encoding for collection video.
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