CU depth-based ALF decision for fast HEVC encoding

In this paper, we propose a coding unit (CU) depth-based adaptive loop filter (ALF) decision method to reduce the encoder complexity. In high efficiency video coding (HEVC), ALF is designed based on Wiener filter to minimize the distortion between the original frame and the coded frame. In order to design the optimal filter for each CU, the filter design process is repeated 12 times per CU. The repetition of the filter design process occupies about 77 percent in the total ALF computation time, which substantially increases the encoder complexity. The proposed method simplifies the filter design with the CU depth-based ALF decision, which is based on the observation by exploiting ineffective computations. Experimental results show that the proposed method reduces the encoding time for the repetition of the filter design process by about 13 percent of that of the HEVC test model (i.e., HM 5.0) with 0.1 percent BD-rate increase.