Abstract: H.264 adopts Unsymmetrical cross Multi Hexagon grid Search（UMHexagonS） algorithm for motion estimation.This paper proposes a new fast adaptive motion estimation algorithm based on UMHexagonS algorithm.The idea of a new adaptive factor is introduced in initial search point prediction step for early termination.Different search patterns are adopted for different search patterns so that the search precision is in accordance with search rate.Experimental results show that the improved strategies can reduce 7%~43% of motion estimation time while keeping the bit rate and PSNR almost unchanged.

Key words: H.264, motion estimation, Unsymmetrical cross Multi Hexagon grid Search（UMHexagonS）, threshold judgement, search pattern

摘要： H.264视频编码采用UMHexagonS运动估计算法，在此基础上提出了一种新的快速搜索算法。该算法在预测起始点处又增加了一个自适应的阈值判断，来判断是否可以立即停止搜索。对于不同的块类型，采用不同的搜索模板，保证搜索精度与速度的一致性。实验结果表明：改进算法与原算法相比，搜索时间减少了7%~43%，而码率和信噪比几乎不变。

关键词: H.264, 运动估计, 非对称十字型多层次六边形格点搜索算法（UMHexagonS）, 阈值判断, 搜索模板