Fast variable-size block motion estimation for efficient H.264/AVC encoding

In this paper, an efficient algorithm is proposed to reduce the computational complexity of variable-size block-matching motion estimation. We first investigate features of multiple candidate search centers, adaptive initial-blocksizes, search patterns, and search step-sizes, to match different motion characteristics and block-sizes. To avoid being trapped in local minima, the proposed algorithm uses multiple candidate motion vectors, which are obtained from different block-sizes. To further reduce the computation cost, a threshold-based early stop strategy according to the quantization parameter is suggested. With adaptive initial block-sizes, a merge-or-skip strategy is also proposed to reduce the computation for the final block-size decision. For the H.264/AVC encoder, simulations show that the proposed algorithms can speed up about 2.6-3.9 times of the original JM v6.1d encoder, which uses fast full-search for all block-sizes, and still maintain a comparable rate-distortion performance.