Revisiting Pre-analysis Information Based Rate Control in x265

Abstract: Due to the excellent compression and high real-time performance, x265 is widely used in practical applications. Combined with CU-tree based pre-analysis, x265 rate control can obtain high rate-distortion (R-D) performance. However, the pre-analysis information is not fully utilized, and the accuracy of rate control is not satisfactory in x265 because of an empirical linear model. In this paper, we propose an improved cost-guided rate control scheme for x265. Firstly, the pre-analysis information is further used to refine the bit allocation. Secondly, CU-tree is combined with the lambda-domain model for more accurate rate control and higher R-D performance. Experimental results show that compared with the original x265, our method can achieve 10.3\% BD-rate gain with only 0.22\textperthousand bitrate error.