优化编码树单元级比特分配算法

Optimized bit allocation algorithm for coding tree unit level

新一代视频编码标准H.266/VVC(Versatile Video Coding)的码率控制算法采用编码参数相互独立的率失真优化技术。然而,同一帧内的编码树单元(CTU)间在空域上相互影响,且存在全局编码参数;同时,CTU级比特分配公式采用近似的编码参数分配比特,进而降低了码率控制精度和编码性能。针对上述问题,提出空域全局优化CTU级比特分配算法RTE_RC(Rate Control with Recursive Taylor Expansion),并通过递归算法逼近全局编码参数。首先,建立空域全局优化比特分配模型;其次,应用递归算法求解CTU级比特分配模型中的全局拉格朗日乘子;最后,优化编码单元的比特分配并对编码单位进行编码。实验结果表明,在低延时P(Prediction)帧(LDP)配置下,与码率控制算法VTM_RC相比,所提算法的码率控制误差由0.46%下降至0.02%,码率节省了2.48个百分点,编码时间下降了3.52%,显著提升了码率控制精度和率失真性能。

It the rate control algorithms of the new generation video coding standard H.266/VVC(Versatile Video Coding),the rate-distortion optimization technique with independent coding parameters is adopted.However,the Coding Tree Units(CTUs)within the same frame affect others in the spatial domain,and there are global coding parameters.At the same time,in the CTU-level bit allocation formulas,approximated coding parameters for bit allocation are used,resulting in the reduction of rate control accuracy and coding performance.To address these issues,a spatial-domain global optimization algorithm for CTU-level bit allocation called RTE_RC(Rate Control with Recursive Taylor Expansion)was proposed,and the global coding parameters were approximated by using a recursive algorithm.Firstly,a globally optimized bit allocation model in spatial-domain was established.Secondly,a recursive algorithm was used to calculate the global Lagrange multiplier in the CTU-level bit allocation formula.Finally,the bit allocation of coding units was optimized and the coding units were coded.Experimental results show that under the Low-Delay Prediction frame(LDP)configuration,compared with the rate control algorithm VTM_RC(Rate Control algorithm Versatile Test Model),the proposed algorithm has the rate control error decreased from 0.46%to 0.02%,the bit-rate saved by 2.48 percentage points,and the coding time reduced by 3.52%.Therefore,the rate control accuracy and rate distortion performance are significantly improved by the proposed algorithm.