IEIE Transactions on Smart Processing and Computing, vol. 5, no. 4, August 2016 http://dx.doi.org/10.5573/IEIESPC.2016.5.4.235 235 IEIE Transactions on Smart Processing and Computing Operation-level Early Termination Algorithm for Inter-predictions in HEVC Chae Eun Rhee Department of Information and Communication, Inha University / Incheon, South Korea chae.rhee@inha.ac.kr Received June 27, 2016; Accepted July 21, 2016; Published August 30, 2016 * Regular Paper Abstract: The emerging High-Efficiency Video Coding (HEVC) standard attempts to improve coding efficiency by a factor of two over H.264/Advanced Video Coding (AVC) at the expense of an increase in computational complexity. Mode decision with motion estimation (ME) is still one of the most time-consuming computations in HEVC, as it is with H.264/AVC. Thus, fast mode decisions are not only an important issue to be researched, but also an urgent one. Several schemes for fast mode decisions have been presented in reference software and in other studies. However, the conventional hierarchical mode decision can be useless when block-level parallelism is exploited. This paper proposes operation-level exploration that offers more chances for early termination. An early termination condition is checked between integer and fractional MEs and between the parts of one partition type. The fast decision points of the proposed algorithm do not overlap those in previous works. Thus, the proposed algorithms are easily used with other fast algorithms, and consequently, independent speed-up is possible. Keywords: HEVC, Inter-prediction, Fast mode decision 1. Introduction H.264/Advanced Video Coding (AVC) [1] was regarded as the state-of-the-art video coding standard and is still widely used for various video applications due to the increasing demand for high-definition (HD) video content. Recently, the next-generation video coding standard [2-4] known as High-Efficiency Video Coding (HEVC) was developed by the ISO/IEC Moving Picture Experts Group (MPEG) and the ITU-T Video Coding Experts Group (VCEG). In the emerging HEVC standard, several new features are introduced, including a coding tree unit (CTU), intra-coding with increased spatial prediction directions, more sophisticated interpolation filters, various in-loop filters, and enhanced entropy coding schemes. In particular, various block sizes, from 8×8 to 64×64, and flexible block size selection schemes for predictions and transforms have been shown to be very suitable for large resolutions. Large resolutions such as 4k×2k and beyond (up to 8k×4k) are challenging targets for new video applications and consumer devices. The HEVC standard aims to double the bitrate reduction offered by H.264/AVC at the expense of an increase in computational complexity. Mode decisions with motion estimation (ME) are among the most time-consuming computations in HEVC, as they are with H.264/AVC. Thus, fast inter-prediction is not only an important issue to be researched but also an urgent one. Extensive research efforts have been conducted to reduce the inter-prediction computational complexity for H.264/AVC. There are roughly three categories of algorithms for fast inter-mode predictions. In the first category, candidate block sizes are determined prior to ME, and prediction operations including ME are performed for only the selected candidate block sizes. For this pre- decision, spatial and/or temporal correlation from neighboring information, motion, or texture characteristics are explored [5-15]. In the second category, the results of the prior predictions are compared and further predictions are determined according to the comparison result. Mode decisions are made in a hierarchical manner [13-20]. In the third category, the fractional ME (FME) calculation is reduced using integer ME (IME) results. Candidate block sizes for FME are selected from the IME results. Or FME computations are reused for other blocks that have an identical integer motion vector (MV) [21-23]. However, these solutions cannot be directly applied to HEVC encoding due to the new coding structures and different data processing procedures, compared to H.264/AVC. HEVC reference software and other recent studies have