无线环境下基于H.264的抗误码技术研究

【作者】 石婧；

【导师】 孙亚民；

【作者基本信息】 南京理工大学 ， 计算机应用技术， 2008， 硕士

【摘要】 随着移动通信网络的发展,数据传输速率的提高以及带宽的增加使得无线环境下视频的传输成为可能。但视频数据量非常庞大,而为移动服务所付费用又与无线链路上传送的数据量成正比,因此,无线视频传输就迫切需要一种高压缩效率的编解码标准,H.264应运而生。但也正因为H.264的高压缩率,去除了尽量多的冗余,加上无线信道传输环境的恶劣,使得压缩的码流对误码非常敏感。所以对H.264编解码标准在无线环境下的抗误码技术进行研究,有着现实的意义和紧迫感。本文首先对视频传输中的各种差错控制、错误检测和错误隐藏技术及应用进行了详细的分析,并针对H.264标准中特有的数据分割、灵活宏块排序(FMO)等差错控制技术及应用进行了深入研究。同时,本文还对基于内容的错误隐藏技术进行了介绍。在对各种抗误码技术进行研究的基础上,本文针对基于图像分割的FMO联合模式差错控制方案中存在的前景分割及码率过高的问题进行了改进和实现。同时利用无线信道仿真工具(MobileIP)搭建实验环境,并按照工具说明对多个标准序列进行了测试。本文从编码比特率、编码时间、解码时间及解码后亮度峰值信噪比(PSNR)等方面对原方案和改进方案进行比较和分析。实验结果表明,本文提出的改进方案能有效地降低编码比特率和解码时间,而且对于大多数序列PSNR值也有所提高,取得较好的视觉效果。抗误码技术多种多样,一个发展的趋势是根据具体的使用环境来自适应地选择合适的方法,或联合使用多种方法。基于内容的错误隐藏方式以良好的性能及更贴近人的视觉特性而受到了越来越多的关注。更多还原

【Abstract】 With the development of mobile communications network, the bandwidth and data transfer rate greatly increase, which make the video transmission over wireless channel possible. However, video data is very large. Meanwhile the payment for the wireless bearer services is proportional to the transmitted data volume on it. Then a codec with high compression efficiency is desired and H.264 came into being. But just because of the high compression ratio which removes as much redundancy as possible, coupled with the error-prone wireless transmission channel, which make the encoded bit stream extremely fragile to various errors. Therefore, research on the error control and concealment of H.264-based wireless applications has a realistic significance and urgency.The dissertation first presents some key technologies during the encoding process. Then various techniques on error-control, error-detection and error-concealment are reviewed and an in-depth analysis of their applications is also explored. Moreover, the dissertation expatiates the error control methodologies, such as Data Partition、Flexible Macroblock Ordering(FMO), which are newly introduced in H.264 standards. Besides, some relative information on content-based concealment is also introduced.On the basis of the work above, this dissertation makes an improvement to the error control program based on picture-partition and FMO to solve the defect of high bit-rate and the improper foreground segmentation. Afterwards, MobileIP, the common test condition provided by JVT, is used to emulate the RTP/IP-based transmission on 3GPP/3GPP2 network. And experiments are made out using various video sequences complying with the proposal of the tool. Then a comparison is performed between the original scheme and the improved one with the aspects of compression ratio, decoding time, PSNR and subjective quality assertion. Results show that the proposed improvement can effectively reduce the bit-rates and decoding time. Also some rising of PSNR and better visual perception are achieved to most of the video sequences.As for the variety of different error resilience tools, a developing trend is to self-adaptively select the appropriate one according to the specific application context, or combine some of them. The content-based error concealment, which outperforms the traditional ones with the ability to obtain closer subject perception, is gaining more and more attention.更多还原