Abstract: Multimedia synchronization is key technology in application of distributed multimedia.Solving the conflicts of synchronization insides and among streams as well as that of user interaction，refining synchronization granularity and improving synchronization precision remain unsolved although great efforts for exploration has been exerted by academic circle.The construction method of bi-layer dynamic synchronous model of multimedia presented in this article realizes multimedia synchronization under two kinds of scales based on two kinds of synchronous points，‘natural synchronous point’ and ’pseudo-synchronous point’，being divided into two layers and taking the two methods of Petri net and Agent.The model handles well with the relation between synchronization inside the stream and that among streams，simplifies re-synchronization after real interaction with users and enhances dynamic synchronous expressive ability of multimedia.

Key words: bi-layer, multimedia, synchronous model, petri net, agent

摘要： 多媒体同步是分布式多媒体应用的关键技术，解决流内、流间及用户交互同步的矛盾，细化同步粒度，提高同步精度，是学术界一直努力探索但至今尚未解决的问题。提出的双层多媒体动态同步模型构建方法，基于“自然同步点”和“准同步点”两类不同同步点，分两个层次，采用Petri网和Agent两种不同方法，在两种不同的尺度下完成多媒体同步。模型较好地协调了流内同步和流间同步的关系，简化了用户实时交互后的再同步，增强了多媒体的动态协同表现能力。

关键词: 双层, 多媒体, 同步模型, Petri网, Agent