Fast CABAC Rate Estimation for HEVC Mode Decision

High efficiency video coding (HEVC) employs highly flexible quad-tree structure and various advanced coding tools targeting for providing significant compression performance as compared to all existing video coding standards. Nevertheless, intensive computational complexity is also required in RD (rate distortion) optimization for achieving the optimal mode. In this paper, fast rate estimation is proposed to skip the actual entropy coding of CABAC (context-adaptive binary arithmetic coding) in RD mode decision. The characteristics of residual syntax elements are first investigated comprehensively and then a high-speed algorithm is constructed to accurately predict the bit-rate, which significantly accelerates the entropy coding with well maintaining video quality. Experimental results demonstrate that the proposed method can reduce the encoding time of CABAC by 62% in average with less degradation in RD performance.