目的 视频编码中传统的快速模式判决算法通常基于对视频源特性的分析,但如果考虑到信道传输中的差错,编码模式的率失真特性就会随之改变,快速模式判决算法的性能也会随之下降,需要考虑丢包环境对快速模式判决算法进行优化。方法 为了解决这一问题,首先分析了丢包环境下各种编码模式的端到端率失真特性,在此基础上提出了一个分层结构的快速模式判决算法。通过快速估计出丢包环境下skip和intra模式的编码率失真代价,进而将模式判决的路径划分为non-intra和non-skip。结果 将本文算法与基于遍历算法的容错视频编码算法进行对比实验,本文算法平均可以降低50%左右的编码时间,同时几乎不会降低率失真性能。结论 实验结果表明,在对丢包环境下端到端率失真代价进行估计的基础上,所提出的分层结构快速模式判决的算法,可以在保证解码端图像质量的同时,显著节省编码时间,满足实时视频通信中对低复杂度和鲁棒性的要求。

Objective Traditional fast-mode decision schemes are commonly designed on the basis of feature analysis of the source videos. However, the rate-distortion behavior of the coding modes changes when channel errors are involved. In this study, we propose a fast-mode decision scheme for H.264 video coding to address the requirements of low complexity and error resilience in real-time video communications.Method We examine the end-to-end rate-distortion (R-D) behavior of various coding modes and derive a hierarchical mode decision scheme. We propose a fast estimation of the coding costs of skip and intra modes in a packet-loss environment and narrow the mode decision into a non-intra or non-skip path. Result The proposed algorithm is implemented in H.264 reference software JM12. The classical error-resilient video coding algorithm that conducts an exhaustive search of all coding modes is used as reference. By efficiently skipping a number of motion estimations and intra prediction mode decisions, the algorithm saves time by approximately 50% without deterioration in R-D performance. Conclusion Experiment results show that the proposed fast-mode decision algorithm based on the estimation of end-to-end R-D cost can achieve significant time saving and retain a good image quality.