Fast mode and depth decision algorithm for HEVC intra coding based on characteristics of coding bits

High Efficiency Video Coding (HEVC) is a promising standard for video compression. In intra prediction, HEVC achieves better compression performance by adopting numbers of new tools such as a more flexible partitioning structure and up to 35 prediction modes. However, these tools also lead to great increase in computational complexity. In this paper, a fast mode and CU depth decision algorithm based on characteristics of coding bits is put forward to speed up the process of HEVC intra coding. The bits number difference for intra prediction mode coding (IPMC) between most probable modes (MPM) and non-MPM modes is exploited to assist early decision making of the optimal mode. Meanwhile, if the percentage of IPMC bits in bitstream is high for specific CUs, early depth termination will be performed since more IPMC bits are needed when depth level increases. Experimental results show that the proposed algorithm can save an average of over 45% encoding time of reference encoder HM16.0 at all intra setting, with the advantage of very little, i.e. 0.32% BD-rate increase.