优化交互响应时间是提高IPTV用户体验质量(QoE)的重要措施.为了减少特技播放过程的交互延迟,提出对媒体随机访问点建立索引的方法,以便媒体服务器通过查找索引表即可实现随机访问点的快速定位和关键帧提取.通过对MPEG-2 TS流的系统层结构和H.264 NAL层的结构分析,探讨了封装H.264视频的TS格式媒体文件的两种关键帧提取方法.鉴于IPTV媒体服务器存储的媒体文件数量庞大,采用Hash的方法建立节目信息索引表,以提高节目信息查找效率.最后给出了在媒体预处理过程中为点播内容建立节目信息索引表和随机访问点索引表以减少IPTV特技播放交互延迟的具体实现方案.方案可行性在与华为合作开发的IMS-based IPTV原型系统得到了验证,测试结果符合三重播放业务QoE的交互响应时间要求.%Optimizing interactive response time is an important measure for improving quality of users' experience. To reduce end-points process delay, client caching delay and acquisition delay of Random Access Point (RAP), a novel method based on building RAP index table was proposed. Media RAP acquisition and key frame abstraction can be quickly done by searching index table. With the analysis of MPEG-2 system layer and H. 264 network abstract layer, two methods of key frame abstraction were given. Whereas there are so many media files stored in media server, program information index built by Hash method was discussed, then program information could be acquired quickly. Based on the index tables of RAP and program information built in pre-processing phrase, trick-play implementation was depicted in detail. Furthermore, the feasibility was verified in the IMS-based IPTV prototype developed by Huawei Technologies Co., Ltd and our laboratory.
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