基于率失真特性的视频编码优化算法

Video coding optimization algorithm based on rate-distortion characteristic

率失真(R-D)优化是视频编码器中一项关键技术,然而当前广泛采用的独立率失真优化远未达到全局最优性能。为了进一步提升高效视频编码(HEVC)的压缩性能,提出了一种结合率失真依赖性和率失真特性的二次编码优化算法。首先,采用原始HEVC的方法对当前帧进行第一次编码,从而得到当前帧消耗的比特数和每个编码树(CTU)单元的率失真模型参数;然后,结合时域依赖率失真优化,根据当前帧比特预算和率失真模型参数计算每个CTU的最佳拉格朗日乘子及量化参数;最后,对当前帧中每个CTU采用不同的优化目标重新编码。实验结果表明,在低延迟B帧和P帧编码配置下,与HEVC基准相比,所提视频编码优化算法在同样编码质量下节省了3.5%和3.8%的码率,获得了显著的率失真性能提升。

Rate-Distortion(R-D)optimization is a crucial technique in video encoders.However,the widely used independent R-D optimization is far from being global optimal.In order to further improve the compression performance of High Efficiency Video Coding(HEVC),a two-pass encoding algorithm combined with both R-D dependency and R-D characteristic was proposed.Firstly,the current frame was encoded with the original method in HEVC,and the number of bits consumed by the current frame and the R-D model parameters of each Coding Tree Unit(CTU)were obtained.Then,combined with time domain dependent rate distortion optimization,the optimal Lagrange multiplier and quantization parameter for each CTU were determined according to the information including current frame bit budget and R-D model parameters.Finally,the current frame was re-encoded,where each CTU had different optimization goal according to its Lagrange multiplier.Experimental results show that the proposed algorithm achieves significant rate-distortion performance improvement.Specifically,the proposed algorithm saves 3.5% and 3.8% bitrate at the same coding quality,compared with the original HEVC encoder,under the coding configurations of low-delay B and P frames.