针对H．264视频编码标准可伸缩扩展部分采用Hierarchical—B结构实现了时域上的可分级特性．同时与传统的IPPP或者IBP编码结构相比，在编码增益上也有较大的提高。但其特殊的预测结构会造成图像质量的抖动，在有快速运动和场景切换时此现象尤甚。提出了一种简单的基于PSNR和MAD的恒定质量控制算法，通过在帧级选择合适的量化参数来限制图像质量的波动范围。该算法在JVT规定的标准基础上进行了仿真，实验结果表明，PSNR的方差大幅减小，并基本接近目标PSNR。

The scalable extension of H.264 video coding standard (SVC) has achievesd temporal scalability using Hierarchical-B structure. Compared to traditional coding structures like IPPP and IBBP, ithas a significant coding gain as well. However, due to its hierarchical prediction dependency, quality fluctuation among consecutive frames may sometimes occur. Such situation usually gets worse when high motion or scene changes exist. In this paper, we propose a simple but effective constant quality algorithm based on PSNR and MAD measures. Restriction to the possible fluctuation is realized by adapting the quantization parameter(QP) at frame level. We simulate our method based on JVT official specification. Experimental results show that our algorithm has greatly reduced the PSNR variance and obtained the target PSNR simultaneously.