Low-complexity merge candidate decision for fast HEVC encoding

This paper presents a low-complexity Merge candidate decision scheme for fast High-Efficiency Video Coding (HEVC) encoding. Merge mode is a new Motion Vector (MV) representation tool that omits signaling of delta MV information of an inter-coded prediction unit (PU) by sending the index of MV to be merged to that inter-coded PU. Although the Merge mode brings significant coding efficiency improvements, the complexity of its Merge candidate decision associated with Rate-Distortion (R-D) cost computation is proportional to the number of Merge candidates. Thus the Merge candidate decision is a complex encoding process. We reveal redundant and unnecessary R-D cost computation for particular Merge candidates through the investigations on correlation between Ground-truth MVs (GMVs) obtained by motion estimation (ME) and Merge candidates as well as on the position occurrences of selected Merge candidates. We propose a low-complexity Merge candidate decision scheme that determines the most favorable Merge candidate from full Merge candidates by using the GMV and the position information of each Merge candidate of an inter-coded PU. Simulation results demonstrate that, relative to HM-9.0 with one Merge candidate (Ref-1), the proposed scheme achieves 0.16%-1.58% B-D rate reduction without increasing encoding time.