中文摘要：

视频点播中的VCR操作对网络带宽的高负载是实际VOD系统需要解决的一个关键问题。为此，基于帧率对用户感受质量影响的分析，提出了一种基于帧率与帧位置联合调整的VCR实现算法。该算法在提出的VCR操作模型中，对快进快退操作增加了带宽与时间约束条件，并在MPEG双向流的基础上，通过调整帧率与播放帧的位置来满足约束条件。实验结果表明，该算法能够在保持较好的用户感受质量下，有效降低了VCR操作对网络带宽的需求。与MPEG双向流算法相比，该算法需要的网络带宽为影片的平均码率的90％左右，且已成功应用于上海高性能宽带网络（863）IPTV示范系统中。

英文摘要：

Due to high bandwidth resource requirement, how to support the digital video cassette recorder （VCR） functionality is a key problem in practical video on demand（VOD） systems. Based on the investigation of the impact of the frame rate on quality of perception（ QoP）, an effective algorithm which selects frames by cooperatively adjusting the frame rate and position is proposed. The proposed algorithm presents a VCR operation model, and adds two constraints conditions to the fast forward and fast backward operations： bandwidth requirement and time limit. Based on MPEG dual-stream, the algorithm meets two constraint conditions by adjusting the frame rate and the frame＇ s position which would be displayed. Simulation results show that the proposed algorithm can effectively reduce the network bandwidth requirement of the VCR operation, while keeping good QoP. The proposed algorithm outperforms the dual bit-stream algorithm, which only needs about 90 percent of the mean bit-rate bandwidth. The method was already successfully deployed in Shanghai national high- tech research and development plan（ 863 ） IPTV systems.