Adaptive inter CU partitioning based on a look-ahead stage for HEVC

Abstract

High Efficiency Video Coding (HEVC) has become the state-of-the-art video coding standard. It outperforms its predecessors by the introduction of new coding tools, such as the new quadtree-based partitioning scheme called the coding tree unit (CTU), which enables a more flexible partitioning of the input frames. However, selecting the optimal partitioning requires the evaluation of numerous possibilities, which involves long computing times that hinder the applicability of the standard in real-world scenarios. With this in mind, the main focus of this paper is on tackling this complexity by means of a fast partitioning and mode decision algorithm based on a look-ahead stage. This stage performs a preliminary motion estimation that provides the motion costs used to build the least-cost quadtree, which is in turn utilized to conduct the encoding itself. On the basis of this quadtree, the encoder may decide to terminate the partitioning early, or to evaluate additional depth levels adaptively. Furthermore, the encoder may omit some prediction modes according to the costs estimated by the look-ahead stage. A thorough experimental evaluation of the algorithm shows that it can reduce the encoding time by 65.33%, at the expense of only a 1.35% BD-rate for the random access configuration. Combined with a fast inter prediction algorithm, this reduction can rise to 70.55%, while the coding efficiency is maintained at a 1.83% BD-rate. When compared with other related works, these results display an excellent trade-off between the two variables.