Fast HEVC Inter CU Decision Based on Latent SAD Estimation

The emerging high efficiency video coding (HEVC) standard has improved compression performance significantly in comparison with H.264/AVC. However, more intensive computational complexity has been introduced by adopting a number of new coding tools. In this paper, a fast inter CU decision is proposed based on the latent sum of absolute differences (SAD) estimation. Firstly, a two-layer motion estimation (ME) method is designed to take advantage of the latent SAD cost. The new ME method can obtain the SAD costs for both the upper CU and its sub-CUs. Secondly, a concept of motion compensation rate- distortion (R-D) cost is defined, and an exponential model is proposed to express the relationship between the motion compensation R-D cost and the SAD cost. Then, a fast CU decision approach is designed based on the exponential model. The fast CU decision is implemented by comparing a derived threshold with the SAD cost difference between the upper and sub SAD costs. Experimental results show that the proposed algorithm achieves an average of 52% and 58.4% reductions of the coding time at the cost of 1.61% and 2% bit-rate increases under the low delay and random access conditions, respectively.