Fast coding structure decision for HEVC inter prediction coding using in-loop filtering, motion prediction and residue information

Abstract

Recently, a new video coding standard, High Efficiency Video Coding (HEVC), has shown greatly improved coding efficiency by adopting hierarchical structures of coding unit (CU), prediction unit (PU) and transform unit (TU). In order to best achieve the coding efficien-cy, the best combinations of CU, PU and TU must be found in the sense of the minimum rate-distortion (R-D) costs. Owing to this, a large computational complexity occurs. Among these CU, PU and TU, the determination of CU sizes most significantly affects the R-D performance of HEVC encoders, which causes large computational costs in operation with PU and TU size de-terminations. In spite of recent works in the complexity reduction of HEVC encoders, most of the research has focused on the complexity reduction with fast CU split in Intra slice coding and with early TU split in both Intra and Inter slices. In this dissertation, we propose a fast and efficient CU encoding scheme based on spa-tio-temporal encoding parameters of HEVC encoders, which consists of an improved early CU SKIP detection method and a fast CU split decision method. For the current CU block under en-coding, the proposed scheme utilizes sample-adaptive-offset (SAO) parameters as the spatial encoding parameter to estimate the texture complexity that affects the CU partition. In addition, the motion vectors, TU size and coded block flag (cbf) information are used as the temporal en-coding parameters to estimate the temporal complexity that also affects the CU partition. The pro-posed scheme effectively utilizes the spatio-temporal encoding parameters which are the by-products during the encoding process of HEVC without additionally required computation. The proposed novel fast CU encoding scheme significantly reduces the total encoding time with neg-ligible RD-performance loss. The experimental results show that the proposed scheme achieves the total encoding time savings of average 49.6% and 42.7% only with average 1.4% and 1.0% bit-rate losses for various test sequences under random access and low delay B conditions, re-spectively. In addition, fast PU mode decision method is included with fast CU split decision. Totally, the experimental results with fast PU mode decision and fast CU split decision method work jointly show 46.9% encoding time saving only with 1.4% bit-rate loss. The proposed scheme has an advantage on implementation for parallel processing in pipeline structures of HEVC encoders due to its independency with neighboring CU blocks.