中文摘要：

H.264视频编码标准对于帧内预测采用了I16×16、I4×4和IPCM三种模式,而前两种模式分别有四种和九种预测方向,这些特性提高了帧内宏块的编码效率,但同时也增加了帧内模式选择的复杂度。提出了一种适用于H.264视频流空间分辨率缩减转码的帧内宏块模式选择算法,主要利用输入码流中的宏块模式信息,推算出下采样后宏块可能的模式及预测方向,从而减少需要计算的宏块模式数目,同时对I4×4宏块采用子块刷新机制,确保转码质量。实验证明,在保持编码效率和视频质量的同时,能有效降低H.264下采样转码过程中帧内宏块模式选择算法的复杂度。

英文摘要：

The H.264 video coding standard adopts some new methods for intra prediction.Though these characteristics enhance the efficiency of coding,it also increases the complexity of intra coding.This paper proposed a fast intra mode decision algorithm of spatial downscaling tanscoding for H.264. Fully used the statistic information of the source video stream to estimate the most possible modes and predict directions.The experimental results show that the proposed algorithms can increase the speed of intra coding significantly with neligibal loss of PSNR and increase of bite-rate.