This article discusses some methods of the implementation of VOD （Video-On-Demand） systems and presents a new scheme called timeshared VOD to implement TVOD （True VOD） system． This scheme which is similar to the multitask system can reduce the costs of content and technology yet provide a service quality that matches user expectations

In the Video on Demand(VoD) system that under the Peer to Peer(P2P) network environment with structure of server and as for the client side s demand on the cache media streaming data,this paper proposes a new prediction double buffer model and gives the corresponding cache replacement algorithm.