SAD reuse in hierarchical motion estimation for the H.264 encoder

The adoption of multiple macroblock partitions with variable block sizes is one of the main reasons behind the superior coding efficiency of H.264 video coding standard. Unfortunately, in the motion estimation phase, repeating sum of absolute difference (SAD) calculations for every possible block size incurs a heavy computational cost for the encoder. In this paper, in order to reduce the encoder complexity, we propose a hierarchical block matching based motion estimation algorithm that uses a common set of SAD computations for motion estimation of different block sizes. Based on the hierarchical prediction and the median motion vector predictor of H.264, the algorithm defines a limited set of candidate vectors; and the optimal motion vectors for all partitions are chosen from this common set. Simulation results show that hierarchical estimation with SAD reuse reduces the total computations by a factor of 17.6 with slight loss in coding efficiency.