Fast inter mode decision for HEVC based on transparent composite model

In comparison with H.264/AVC, the newest video coding standard, High Efficiency Video Coding (HEVC), improves video coding rate distortion (RD) performance, but at the price of significant increase in its encoding complexity, due to its complicated inter mode decision process. In HEVC inter coding, the actual RD costs of all combinations of coding units (CUs), prediction units (PUs), and transform units (TUs) have to be computed and then the combination (i.e., mode) with the minimum cost is selected and encoded. To reduce the inter mode decision complexity in HEVC while maintaining its coding efficiency, in this paper, a fast inter mode decision method based on a newly proposed Transparent Composite Model (TCM) is developed. Spatially and temporally homogeneities are identified by TCM, and then used, together with spatiotemporal correlation between CUs, to determine PU and CU partitions so that cost computations of unnecessary modes can be skipped. Experimental results show that, for the low delay main test configuration of HEVC, our method reduces, on average, the encoding time by 60.71% with an insignificant loss in coding efficiency (1.06% BD-Rate increase).