Hierarchical Structure-Based Fast Mode Decision for H.265/HEVC

The mode decision strategy adopted in the High Efficiency Video Coding test model increases the complexity drastically. In this paper, we present a course of low-complexity fast mode decision algorithms. First, the depth information of the colocated block from a previous frame is used to predict the size of current block. Next, for a certain sized block, the inter-prediction residual is analyzed to determine whether to terminate the mode decision process or to skip unnecessary modes and split the block into smaller sizes. After inter-prediction, a hardware-oriented low-complexity fast intra-mode decision algorithm is proposed. A fast discrete cross difference is adopted to detect the dominant direction of the block. In addition, four simple but efficient early termination strategies are proposed to terminate the rate-distortion optimization process properly. The simulation results show that these proposed algorithms reduce the encoding time by 54.0%-68.4% without incurring any noticeable performance degradation. Hardware synthesis results demonstrate that the proposed fast intra-mode decision algorithm can be easily implemented on a hardware platform with fewer resources consumed.