H.264/AVC视频编码标准采用码率—失真度最优化(RDO)算法，以保证更高的压缩效率和更好的图像质量,但同时也大大增加了编码器的复杂度和运算负担。本文提出了一种新型的帧内预测模式的快速选择算法，该算法基于图像内部信息的变化剧烈程度进行判断，并通过方向矢量来减少候选帧内预测模式。试验结果表明，该算法可以将整个编码时间减少到原来采用RDO算法时的40%~50%，而且和RDO算法比较，最终压缩后的视频图像质量基本没有下降。

In order to guarantee higher compression efficiency and video quality, a robust rate-distortion optimization(RDO) is employed in H.264/AVC video coding standard, which is jointly developed by ITUT and MPEG. According to the specification of RDO, all of the prediction modes have to be tried exhaustively in order to find the best mode. As a result, the computational complexity of the mode decision is extremely high and is not suitable for the real time service, such as video conference.This paper proposes a fast intra prediction modes decision algorithm based on the discrepancy within the video picture. In addition, the Direction-Vector based preferred modes selection method is introduced in the proposed algorithm to reduce the candidate modes to be tested. Experimental results are given to demonstrate that our proposed algorithm achieves a reduction of processing time by 40%~50% as compared with the current RDO optimized mode decision with little quality degradation.