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各媒体对象

Several definitions for the terms multimedia application and multimedia systems are described in the literature. Three criteria for the classification of a system as a multimedia system can be distinguished: the number of media, the types of supported media and the degree of media integration. Combining all three criteria, we propose the following definition of a multimedia system: a system or application that support the integrated processing of several media types with at least one timetimedependent medium .
• 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,KG89,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.
Type of media Hybrid System
Time-Dependent and time-independent Time-dependent
Integrated, Digital System Audio/Video Applications VideoServer
Time-independent
下一层次的同步是为时间相关、时间无关媒 体以及用户交互的同步提供动态运行支撑 [MHE93,Bla92,KC89,Lit93]，其目标是：如 [MHE93,Bla92,KC89,Lit93]，其目标是：如 果遇到时间相关媒体对象中预先定义好的同 步点，则在一个用户可以忍受的时间间隔内 来启动终止媒体无关对象的表现。
op Publishing
Text Editors No Media Integration Full Media Integration
n media
1 media
Number of Media
Integration of Media
Figure 15.1: Classification of media use in multimedia systems
操作系统和低层的通信主要负责处理单个媒 体流，以避免某一媒体在单元的表现中出现 抖动和跳跃[NS95c,DHH94,PZF94,OP93], 抖动和跳跃[NS95c,DHH94,PZF94,OP93], 例如，在音频裁剪中，如果音频的表现波停 顿或“咔嗒声”所打断，那么用户将会很不 满意。
• 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 audio presentation is interrupted by pauses or if clicks result in short gaps in the presentation of the audio clip.
多媒体系统
关于多媒体应用和多媒体系统有很多定义， 关于多媒体应用和多媒体系统有很多定义，区分一 个系统是否为多媒体系统的三条标准是：媒体的数目、 个系统是否为多媒体系统的三条标准是：媒体的数目、 支持媒体的类型和媒体的一体化程度。 支持媒体的类型和媒体的一体化程度。 综合上述三个标准，我们给出了如下的多媒体 系统定义：多媒体系统是指支持多种类型媒体一体化 处理的系统或应用，且其中至少有一种媒体是时间相 关媒体。
媒体对象间的同步包括时间相关和时间无关 的媒体对象之间的同步，关于连续媒体对象 同步的一个详细例子是：在电视中，视觉信 息与听觉信息的同步。在多媒体系统中，必 须为音频和运动图像提供相似的同步机制。 关于时间相关媒体和时间无关媒体的同步关 系的例子是幻灯片的放映，在幻灯片的放映 时要与对其内容进行介绍或评价的音频同步。 在多媒体系统中实现幻灯片的放映时，其图 形显示必须与音频流中的适当单元进行同步。
多媒体同步由很多系统部件来支撑和体现，包括 操作系统、通信系统、数据库、文档、甚至一些 具体应用，因此，多媒体系统中的同步必须在多 个层次予以考虑。
• Synchronization is addressed and supported by many system components including the operating system, communication system, databases, documents and even often by applications. Hence,synchronization must be considered at several levels in a multimedia system.
基本同步问题
一体化媒体处理是多媒体系统的一个重要特 性，要求一体化处理的主要原因是被编码为 媒体对象的信息的内在相关性，这些相关性 必须反映在一体化处理中，包括媒体的存储、 操作、通信和抓获，特别是媒体对象的表现。
• Integrated media processing is 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, capturing and, in particular, the presentation of the media objects.
Synchronizations between media objects comprises relations between time-dependent media objects and timetimetime-independent media objects. A daily example of synchronization between continuous media is the synchronization between the visual and acoustical information in television. In a multimedia system, the similar synchronization must be provided for audio and moving pictures. An example of temporal relations between time-dependent media and time-independent timetimemedia is a slide show. The presentation of slides is synchronized with the commenting audio stream. To realize a slide show in a multimedia system., the presentation of graphics has to be synchronized with the appropriate units of an audio stream.
The word synchronization refers to time. Synchronization in multimedia systems refers to the temporal relations between media objects in the multimedia system. In a more general and widely used sense some authors use synchronization in multimedia as comprising content, spatial and temporal relations between media objects. We differentiate between time-dependent and timetimetimeindependent media objects. A time-dependent media timeobject is presented as a media stream. Temporal relations between consecutive units of the media stream exist. If the presentation durations of all units of a time-dependent media object are equal, it is timecalled continuous media object. A video consists of a number of ordered frames; each of these frames has a fixed presentation duration. A time-independent timemedia object is any kind of traditional media like text and images. The semantic of the respective content does not depend upon a presentation according to the time domain.