Abstract: The scalable extension of H.264 video coding standard（SVC） achieves temporal scalability using Hierarchical-B structure.Compared with traditional coding structures like IPPP or IBBP，it obtains a significant coding gain.In the structure，the output rate is controlled by adaptively adjusting the coding fame rate.Thus，the variance of bandwidth can cause frame rate fluctuation and temporal discontinuity.An optimized rate control algorithm is proposed.The output rate is adjusted for each layer according to its importance.The coding frame rate is also considered to limit the discontinuity.Simulation results show that the proposed algorithm effectively controls the rate with less frame rate fluctuation，and achieves an average PSNR gain of 0.45 dB compared with some other methods.

Key words: Scalable Video Coding（SVC）, rate control, Rate Distortion Optimization（RDO）, sliding window

摘要： H.264/AVC可伸缩视频编码系统（SVC）在时间域采用的可分级B帧（Hierarchical B）结构，与传统的IPPP或者IBBP编码结构相比，编码性能有较大提高。其采用调整单位时间内编码和显示的图像帧数来适应不同的码率。但信道带宽变化较大时，帧率波动较大，会造成视频的不连续性。因此，针对各分层不同特点给出相应的码率控制方案，并通过对B帧选择合适的量化参数限制图像帧率的波动范围。实验结果表明该算法能够有效地控制码率，帧数波动小，视频质量较好，与其他同类算法相比PSNR平均能提高0.45 dB。

关键词: 可伸缩编码, 码率控制, 率失真优化, 滑动窗口