运动估计是视频编码中举足轻重的环节，其性能的优劣很大程度上影响着编码质量。为此提出了一种基于方向判断的自适应运动估计快速搜索算法。该算法充分考虑序列自身的运动属性，利用相邻块运动矢量场的分布特性，根据相邻块运动矢量的相似程度自适应地设定阈值来判断静止块，并且对预测运动矢量进行方向的判断，使用方向性的模板搜索最优点。与以往算法相比，该算法考虑了图像序列本身的特性，具有更高的灵活性。仿真结果表明，在基本不损失性噪比的情况下，该算法对不同序列均有效的降低了运算量。

Motion estimation (ME) plays an important role in video coding system, since it could significantly affect the output quality of an encoded sequence. This paper proposes a fast adaptive ME algorithm based on the judgment of the predictive motion vector (PMV). This proposed algorithm takes advantage of the correlation of neighboring blocks to adaptively decide the threshold for judging the stationary regions. And this algorithm sorts the PMV into several regions by its direction and uses different search patterns, respectively. Compared with the former algorithm, this algorithm considers the characteristic of different sequences and thus, it is more flexible than before. Experimental result shows that this algorithm reduces computation complexity variously for different sequence under the premise that the PSNR does not lose.