【作者】 郭映；

【导师】 李桂苓；

【作者基本信息】 天津大学 ， 信号与信息处理， 2005， 博士

【摘要】 随着数字音、视频及多媒体技术的发展,迫切需要压缩巨大的视频信号数据量,适用于不同应用领域的MPEG-1、MPEG-2、MPEG-4、H.26x等国际编码标准应运而生。另一方面,为了适应用户终端的多样性以及网络自身的传输特性,需要将已压缩的视频码流进行转换,即转换编码,以实现网络间资源共享。将经过压缩的视频数据进行远程传输时,需要考虑网络拥塞、信道带宽及终端处理能力。码率控制策略的目的就是通过调整编码端的编码参数,保证信道正常传输,并获得尽可能好的图像质量。作为对视频转换编码及码率控制研究的基础,本文首先介绍了几种主要的视频编码标准。接着,对影响输出码率的因素进行了分析。第三章讲述了几种典型视频编码标准建议的码率控制策略,为提出新控制算法打下基础。论文从低码率视频编码码率控制入手,提出了码率控制新算法,包括:帧层比特率分配策略优化,即根据目标码率的要求,给不同类型帧分配不同编码比特数,以减少跳帧数;利用人的视觉特性,提出基于宏块层的码率控制策略,即引入宏块层视觉修正因子及视觉加权矩阵;通过分析图像失真与量化顺序之间的关系,以及视频编码标准中的比特流语法,进一步提出了一种量化参数自适应宏块层码率控制新算法,该算法与传统量化顺序以扫描为基础不同,是按复杂度确定宏块量化顺序。实验结果显示,新算法的主、客观图像质量均有所改善。本文在研究转换编码码率控制策略前,先对转换编码结构进行了详细介绍,以搭建一个良好的实验平台。通过分析不同编码标准的特点、码流结构和解码信息,提出了适用于异类转换编码的码率控制策略。文中以MPEG-2到H.263/MPEG-4转换编码为例,利用MPEG-2解码信息,结合H.263/MPEG-4编码标准建议的码率控制策略及本文提出的改进算法,实现了输出码率的有效控制,并改善了重建图像的主、客观质量。更多还原

【Abstract】 Along with digital AV and multimedia technology developing, largenumbers of video datum need to be compressed. At present, the InternationalCoding Standards, such as MPEG-1, MPEG-2, MPEG-4, H.26x have beenestablished and applied to different application areas. In order to adapt toheterogeneous client terminals and transmission characteristic of networks,pre-encoded video should be transcoded into another coding format. So, theresources of networks can be shared.When the video datum is transmitted far from here, network congestion,channel bandwidth and disposal ability of terminal should be considered. Targetof rate control is to ensure the channel normal and obtain better image quality byadjusting the parameters of encoder.As the basis of the following research on transcoding and rate control,several related video coding standards are introduced in this thesis first. And then,the effect factors of the bit rate are analyzed. A few typical methods of ratecontrol are expatiated in the third chapter, which are theories basis of the newarithmetic.The research in this thesis starts with rate control in low bit rate. The newarithmetic includes bit allocation optimizing in frame layer, namely, differentbits are allotted to different frames in order to decrease the number of skippingframes. Using human visual character, visual modified factor and matrix areintroduced in macroblock layer. By analyzing the relationship between imagedistortion and quantizing order, along with bit stream syntax, a novel macroblocklayer rate control strategy is proposed. This strategy in which quantization orderis based on complexity is different from traditional method in which quantizationorder is based on scan order. The results of experiments show that subjectiveand objective qualities of the new method are improved.Before the research of rate control in transcoding, the transcodingframework is introduced first. The rate control scheme in heterogeneoustranscoding is presented by the encoding characters in different standards, bitstream architecture and decoded information analyzed and studied. For example,MPEG-2 transcoding to H.263/MPEG-4 is taken into account in this paper. Byutilized decoded information in MPEG-2 and combined rate control strategy inH.263/MPEG-4, the new rate control scheme implements effectively control andimproved subjective and objective quality.更多还原