帧间模式选择是H264编码器中最耗时的部分。提出一种基于全零块和运动方向一致性的新的快速模式选择算法。该算法首先定义了绝对全零块充分条件和相对全零块必要条件，并按照这两个条件将宏块分成4大类，然后在每一大类中利用宏块周边块的运动状态及该宏块在SKIP模式下的率失真代价将宏块进一步分类，缩小该宏块的候选预测模式范围。实验结果表明，该算法能够极大提高帧间模式选择的速度，并且所带来的PSNR损失和码率增加几乎可以忽略。

Inter frame mode decision is the most time consuming part in H264. A novel fast mode decision algorithm based on all zero block and consistency of moving direction is proposed in this paper. Firstly, the sufficient condition of absolute all zero block and the necessary condition of relative all zero block are defined to divide the MB into four classes. Secondly, in each class, the moving state of neighboring MB and the SKIP RD cost of this MB are used to further classify the MB into some categories so that the range of candidate modes can be narrowed. The experimental results have shown that the proposed algorithm can speed up inter frame mode decision greatly and incurred loss in PSNR and increment in rate can almost be neglected.