Analysis and optimization of x265 encoder

x265 is an open-source encoder project which aims to deliver the world's fastest and most computationally efficient HEVC encoder. Although x265 has been developed efficiently with many optimization techniques, it is still not able to encode HD videos in real time even at its faster setting. In this paper, we deeply investigate the encoding framework and computational complexity of x265, and find that RDO process is the most time consuming part. Then, an efficient prediction scheme is proposed which includes decreasing the number of RDO times, early skip detection and fast intra mode decision. Experimental results show that the proposed method improves the speed of x265 from 19.86fps to 37.76fps for HD test sequences, i.e., 47.44% complexity reduction, with only 1.37% BDBR coding performance loss.