Fast Intra Mode Decision for High Efficiency Video Coding (HEVC)

The latest High Efficiency Video Coding (HEVC) standard only requires 50% bit-rate of the H.264/AVC at the same perceptual quality, but with a significant encoder complexity increase. Hence, it is necessary and inevitable to develop fast HEVC encoding algorithms for its potential market adoption. In this paper, we propose a fast intra mode decision for the HEVC encoder. The overall fast intra mode decision algorithm consists of both micro- and macro-level schemes. At the micro-level, we propose the Hadamard cost-based progressive rough mode search (pRMS) to selectively check the potential modes instead of traversing all candidates (i.e., up to 35 in HEVC). Fewer effective candidates will be chosen by the pRMS for the subsequent rate-distortion optimized quantization (RDOQ) to derive the rate-distortion (R-D) optimal mode. An early RDOQ skip method is also introduced to further the complexity reduction. At the macrolevel, we introduce the early coding unit (CU) split termination if the estimated R-D cost [through aggregated R-D costs of (partial) sub-CUs] is already larger than the R-D cost of the current CU. On average, the proposed fast intra mode decision provides about 2.5 × speedup (without any platform or source code level optimization) with just a 1.0% Bjontegaard delta rate (BD-rate) increase using the HEVC common test condition. Moreover, our proposed solution also demonstrates the state-of-the-art performance in comparison with other works.