Early MERGE Mode Decision Based on Motion Estimation and Hierarchical Depth Correlation for HEVC

The high efficiency video coding (HEVC) is the latest video coding standard, which adopts the quadtree structure based coding tree unit (CTU) to improve the coding efficiency. In the HEVC encoding process, the CTU is recursively split into the 8×8 size coding units (CUs) from the 64×64 size CU. Along with the increased number of the sizes of the CUs, the number of coding modes has been greatly increased, which results in high computational complexity in the HEVC encoder. In this paper, we propose an early MERGE mode decision algorithm to reduce the computational complexity of the HEVC encoder. Firstly, based on the all-zero block (AZB) and the motion estimation (ME) information of the INTER 2N×2N mode, an early MERGE mode decision is proposed for the root CUs (i.e., 64×64 size CUs). Then, an early MERGE mode decision is proposed for the children CUs (i.e., 32×32, 16×16, and 8×8 size CUs) by considering the mode selection correlation between the root CU and the children CUs. To maximize the computational complexity reduction, when the root CUs are encoded in the non-MERGE modes, the AZB and the ME information are also used for early termination of the children CUs. Experimental results demonstrate that compared to the state-of-the-art published method, the proposed algorithm can achieve about 35% encoding time on average saving while the rate distortion performance degradation is negligible.