RESEARCH ON AMULTIPOINT COMMUNICATION FOR STORED VIDEO

我们的研究项目旨在开发一种通过高速分组链路传输存储在视频数据库中的多路视频信号的方法。本课题取得的主要成果如下：(1)研究发现，视频峰值信噪比(PSNR)与码率之间的关系可以用分段线性关系来表示。该关系的参数取决于视频场景的场景特征。(2)提出了基于该关系的每一个MPEG视频流的最佳带宽分配方法。这里，考虑每个场景的PSNR-码率关系，分配带宽，使最大的PSNR降幅最小。(3)当每个视频流由多个场景组成时，提出了动态带宽分配方法，得到每个场景的PSNR-码率关系，并在场景切换后重新分配带宽。(4)制作了多路视频流传输的原型系统，发现原型运行良好。(5)在直播媒体传输的情况下，在传输之前很难获得PSNR-码率关系。提出了一种适用于直播媒体的带宽分配方法，利用新场景的短期信息来估计PSNR-码率关系。(6)基于IP协议的重传时延降低了视频流的传输质量。我们针对真实类型的媒体开发了新的协议，通过重复和终止协议来减少重传延迟。(7)提出了新的视频检索和分发方法，使IP网络上的视频传输服务更加有效。

Our research project aims at developing the method to transmit multi number of video signals stored in video database through high speed packet link. Results obtained in this project are summarized as follows ;(1)We found that relation between PSNR(Peak Signal to Noise Ratio) of MPEG video and bitrate can be represented by piecewise linear relation. Parameter of this relation depends on scene characteristic of video scene.(2)We proposed the optimum band allocation method for each MPEG video streams based on the relation. Here, considering PSNR-bitrate relation of each scene, bandwidth is allocated so that the largest PSNR degradation is minimum.(3)When each video stream consists of plural number of scenes, dynamic bandwidth allocation method is developed, where PSNR-bitrate relation is obtained for each scene and bandwidth is reallocated just after scene change.(4)We have made prototype system of the multi-channel video stream transmission and found that the prototype works well.(5)In case of live media transmission, it is not easy to obtain PSNR-bitrate relation before transmission. We have developed the bandwidth allocation method for live media, where PSNR-bitrate relation is estimated using the short term information of new scene.(6)Video stream transmission quality is degraded based on retransmission delay of IP protocol. We have developed novel protocol for real type media, where retransmission delay decrease by repeating and terminating protocol.(7)We have developed novel method of video retrieval and distribution so that video transmission service over IP network is more effective.