High Efficiency Video Coding (HEVC or H.265), the latest international video coding standard, displays a 50% bit rate\nreduction with nearly equal quality and dramatically higher coding complexity compared with H.264. Unlike other\nfast algorithms, we first propose an algorithm that combines the CU coding bits with the reduction of unnecessary\nintra-prediction modes to decrease computational complexity. In this study, we first analyzed the statistical relationship\nbetween the best mode and the costs calculated through Rough Mode Decision (RMD) process and proposed an\neffective mode decision algorithm in intra-mode prediction process. We alleviated the computation difficulty by\ncarrying out the RMD process in two stages, reducing 35 modes down to 11 modes in the first RMD process stage,\nand adding modes adjacent to the most promising modes selected during the first stage into the second RMD stage.\nAfter these two stages, we had two or three modes ready to be used in the rate distortion operation (RDO) process\ninstead of the three or eight in the original HEVC process, which significantly reduced the number of unnecessary\ncandidate modes in the RDO process. We then used the coding bits of the current coding unit (CU) as the main basis\nfor judging its complexity and proposed an early termination method for CU partition based on the number of coding\nbits of the current CU. Experimental results show that the proposed fast algorithm provides an average time reduction\nrate of 53% compared to the reference HM-16.12, with only 1.7% Bjontegaard delta rate increase, which is acceptable\nfor Rate-Distortion performance.
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