同步是一个与时间相关的概念多媒体系统中的同步主要指

1、媒体对象中各单元的表现间隔完全相同，则称之为连续媒体对象，如视频，它包括一系列的有序帧，每一帧有一固定的表现间隔。时间无关媒体则是指像文本、图像任何一种传统的媒体对象，其各自的内容含义及其表现不依赖于时间。Synchronization is addressed and supported by many system components including the operating system, communication system, databases, documents and even often by applications. Hence,synchronization

2、 must be considered at several levels in a multimedia system.The operating system and lower communication layers handle single media streams with the objective to avoid jitter at the presentation of the units of one media stream (e.g.,NS95c,DHH94,PZF94,OT93). For example, users will be annoyed if an

3、 audio presentation is interrupted by pauses or if clicks result in short gaps in the presentation of the audio clip. The next level holds the run-time support for the synchronization between time-dependent and time-independent media together with the handling of user interactions(e.g.,MHE93,Bla92,K

4、G89,Lit93). The objective is to start and stop the presentation of the time-independent media within a tolerable time interval, if some previously defined points of the presentation of a time-dependent media object are reached. 多媒体系统 Integrated,Digital SystemHybrid SystemAudio/VideoApplicationsDeskt

5、opPublishingVideo-ServerTextEditorsTime-Dependentand time-independentTime-dependentTime-independentn media1 mediaFull MediaIntegrationNo MediaIntegrationNumber of MediaIntegration of MediaFigure 15.1: Classification of media use in multimedia systemsType of media基本同步问题Integrated media processing is

6、an important characteristic of a multimedia system. The main reasons for these integration demands are the inherent dependencies between the information coded in the media objects. These dependencies must be reflected in the integrate processing including storage, manipulation, communication, captur

7、ing and, in particular, the presentation of the media objects. Content Relations Content relations define a dependency of media objects from objects from some data.Spatial Relations The spatial relations that are usually known as layout relationships define the space used for the presentation of a m

8、edia object on an output device at a certain point of time in a multimedia presentation. If the output device is two-dimensional(e.g.,monitor or paper), the layout specifies the two-dimensional area to be used.Temporal Relations Temporal relations define the temporal dependencies between media objec

9、ts. They are of interest. Whenever time-dependent media objects exits.现场直播同步和人工合成同步The live and synthetic synchronization distinction refers to the type of the determination of temporal relations. In the case of live synchronization, the goal of the synchronization is to exactly reproduce at a prese

10、ntation the temporal relations as they existed during the capturing process. In the case of synthetic synchronization, the temporal relations are artificially specifiedLG90b.This example covers two live synchronization aspects: video conference demands lip synchronization of the audio and video conf

11、erence, and the movement of the mouse pointer must be synchronized to the corresponding explanation given in the video conference. In the case of synthetic synchronization, temporal relations have been assigned to media objects that were created independently of each other. The synthetic synchronization is often used in presentation and retrieval-base systems with stored data objects that are arranged to provide new combined multimedia objects. SourceSinkFigure 1