视频编码传输的容错纠错优化方法

【作者】 陈云鹏；

【导师】 张培仁；

【作者基本信息】 中国科学技术大学 ， 模式识别与智能系统， 2006， 博士

【摘要】 由于数字压缩视频对于传输差错极为敏感，比特差错将会导致视频图像质量显著下降，因此如何在具有时变、高误码特征的无线信道上实时、可靠的传输视频数据，提高视频通信质量成为一项重要课题。本文深入研究了差错信道下的视频传输所面临的问题，并提出多种容错或纠错的优化算法。以下是本文提出的四种容错纠错优化方法。 传统的视频码率控制在差错信道上工作时具有这样两个缺点：差错信道上纠错编码导致信道实际的传输码率大于视频编码的设定码率，从而超出信道带宽限制；纠错编码在信道误码率很高时，占用过大带宽。针对这些问题，本文提出一种面向无线信道的码率控制方法，该方法具有这样一些特点：综合了纠错编码和视频编码；混合FEC／ARQ的纠错编码，具有根据信道状况自适应选择最优纠错模式的能力；优化的带宽资源分配，建立率失真模型优化纠错编码和视频编码的比特分配。 参考帧选择是一种降低图像错误扩散，增强视频抗差错能力的有效方法。原有的参考帧选择方法具有复杂度高，编码效率低的特点。为解决这些问题，本文提出一种基于率失真优化、低复杂的参考帧选择方法。该方法通过在编码器上同步解码的误码掩盖过程，使得错误掩盖图像也可作为可选参考帧，增加了编码效率。此外，该方法使用率失真优化方法选择参考图像，进一步增加了编码效率。在率失真优化的过程中，使用图像差值的预测值代替运动估计，大大简化了系统的计算复杂度。 多描述视频编码是一种面向多信道传输的视频编码方法。它通过多信道传送多个同等重要的视频流，来增强视频的抗差错能力。多描述编码存在一个重大问题，即当差错发生时，编解码器上的参考图像会产生失配，这样将引起图像错误扩散。本文提出一种基于误码掩盖补偿的多描述视频编码方法。该方法传输错误掩盖图像与理想图像之间的差值到解码器，理想状态下，解码器可利用这些差值完全无损的恢复错误图像。为提高这种方法的编码效率，本文面向差错信道，进一步提出自适应调节补偿程度的优化方法。通过自适应调节，解码器在有限带宽下，可获得最优的图像质量。 在IP分组交换网络中，一旦发生误码，整个报文将被丢失，这样的工作机制将丢弃报文中很多有用信息。针对这个问题，本文提出一种联合信道编码和多报文解码的优化方法。该方法通过跨层优化，修改网络协议层，并在信道纠错编码中综合使用比特FEC和报文FEC。通过上述优化，解码器可以收到误码报文。在视频解码过程中，解码器利用报文FEC产生的多个报文解码，从而充分利用了误码报文中的有用信息，有效增加了解码成功率。 本文的仿真实验表明了上述四种优化方法的有效性。更多还原

【Abstract】 Compressed video stream is highly sensitive to bit error. When it is transmitted in error-prone channel, picture is damaged too seriously to acceptable Wireless channel is a kind of error-prone channel. It is characterized by state variance and high error rate. How to increase error-resilience is one important work for wireless video communication application. In this thesis, we deep investigate the problem in video transmission, and propose four optimal error-resilient schemes.Traditional video rate control scheme has two disadvantages for error-prone network: first, the error correction coding makes rate control buffer overflow, and increases the number of skipped frames; second, the error correction coding uses too much bandwidth in high error rate channel. In order to resolve above two problems, one rate control scheme is proposed for wireless channel. The scheme is of these characters: joint error correction and video coding; hybrid FEC/ARQ error correction coding; optimal bit allocation between error correction coding and video coding by end to end rate-distortion formula.RPS (Reference picture selection) is one of effective schemes for video error-resilience. It selects appropriate reference picture to cease error propagation. RPS is of high complexity and low efficiency. In this thesis, an optimal low-complexity RPS scheme is proposed. Firstly, the encoder performs error concealment steps the same as the decoder on the basis of the feedback information. Secondly, the encoder selects an optimal reference picture between reconstructed error picture and preceding picture by proposed rate-distortion algorithm. In above process, picture error variance is predicted linearly to decrease the number of motion estimation process, and then computation complexity is lowered.MDVC (Multiple description video coding) is for multiple channels system. In this system, multiple equal important streams are transmitted in different channels. MDVC has one well-known disadvantage: Bit error causes the mismatch of reference picture and degrades the picture quality. To solve this problem, an error compensation MDVC scheme is proposed. In this scheme, error compensation information is transmitted also with generic description information. Description decoder decodes error compensation information to reconstruct the error picture. Additional, a bit allocation algorithm is proposed to adjust error compensation degree adaptive to the channel state.In erasure channel such as IP channel, error packet is whole discarded. In order to make full use of correct bits in error packet, multiple packets decoding scheme is proposed Firstly, through cross-layer optimization and bit level FEC coding, decoder could receive error packets. Secondly, by packet level FEC coding, decoder could decode multiple error packets.Experiments show all of the above four optimal schemes could improve picture quality greatly.更多还原