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1、Chapter 6 Synchronization,Prof. Guohui Li Doctor. Zhihui Xiong Department of Management Science and Engineering National University of Defense Technology Spring 2010,COURSE 600-081205602,MMCN-Chapter6,2,From users perspective, Multimedia means that information can be represented through audio and /o
2、r video, in addition to text, image, graphics and animation.,Review: What is Multimedia,From the technical perspective, the timing and integration requirement among all components of the media is the major challenge.,MMCN-Chapter6,3,Chapter 6,6.1 Introduction 6.2 Basic synchronization issues 6.3 Int
3、ra- and inter-synchronization 6.4 Live and synthetic synchronization The reference: Ralf Steinmets. Multimedia: computing, communications and applications. Prentice Hall, 1995.,MMCN-Chapter6,4,6.1 Introduction,1. Basic concept The word synchronization refers to time,MMCN-Chapter6,5,6.1 Introduction,
4、synchronization in multimedia systems refers to the temporal relations between media objects in the multimedia system.,A time-independent media object: any kind of traditional media like text and images. The semantic of the content does not depend on a presentation according to the time domain.,A ti
5、me-dependent media object: presented as a media stream. Temporal relations between consecutive units of the media stream exist. Such as: video, audio, animation,MMCN-Chapter6,6,6.1 Introduction,Synchronization between media objects comprises time relations between time-dependent media objects and ti
6、me-independent media objects. e.g., video and audio in TV e.g., audio and slides in a presentation.,MMCN-Chapter6,7,6.1 Introduction,2. Synchronization level Why? Since synchronization is addressed and supported by many system components, including the operating system, communication system, databas
7、e, documents and even often applications. Hence, synchronization must be considered at several levels in a multimedia system.,MMCN-Chapter6,8,6.1 Introduction,2. Synchronization level Including: 1) operating system and communication level; 2) application level. Operating system and communication lev
8、el handle single media streams with the objective to avoid jitter at the presentation. e.g., users will be annoyed if an audio presentation is interrupted by pauses.,MMCN-Chapter6,9,6.1 Introduction,2. Synchronization level Application level synchronization of multiple media streams：objective is to
9、maintain the temporal relations between various streams. e.g. lip synchronization (对口型) synchronization between time-dependent and time-independent media together with the handling of user interactions. Objective is to start and stop the presentation of the time-independent media along with time-dep
10、endent media object within a tolerable time interval, e.g., slides show with audio comment synchronously.,MMCN-Chapter6,10,6.1 Introduction,3. Temporal relations specification implicit: e.g., audio/video recording and playback. Explicit: e.g., presentations like this lecture.,MMCN-Chapter6,11,6.2 Ba
11、sic Synchronization Issues,1. Content relations it defines a dependency of media objects from some data. the same data can be presented in two different way, such as spreadsheet and graphic.,e.g. car shopping data “Quarter1 20, Quarter2 24, Quarter3 16, Quarter4 27”,MMCN-Chapter6,12,6.2 Basic Synchr
12、onization Issues,2. Spatial relations also known as layout relations. They define the space used for the presentation of a media object on an output device at a certain point of time in a multimedia presentation. Two-dimensional or three-dimensional output device.,MMCN-Chapter6,13,6.2 Basic Synchron
13、ization Issues,3. Temporal relations define the temporal dependencies between media objects. Comment content and spatial relations are well-known from publishing and integrated application systems with spreadsheets, graphical tools and word processing system. Key aspect in MM system is the temporal
14、relations.,MMCN-Chapter6,14,6.3 Intra- and Inter- Synchronization,1. Intra-object synchronization: the time relation between various presentation units of one time-dependent media object.,frames,t,Each of frames must be displayed for 40ms at a rate of 25 fps.,MMCN-Chapter6,15,6.3 Intra- and Inter- S
15、ynchronization,2. Inter-object synchronization: the time relation between various media objects.,audio1,video,audio2,P2,animation,t,t0,t1,t2,t3,t4,P1,t5,MMCN-Chapter6,16,6.3 Intra- and Inter- Synchronization,3. Time-dependent Presentation Units time-dependent media objects usually consist of a seque
16、nce of information units. Such information units are known as Logical Data Units (LDU). In many cases, several granularity levels of LDU in a media object exist. For example: video - scenes - shots - frames - pixels.,MMCN-Chapter6,17,6.3 Intra- and Inter- Synchronization,The levels of granularity imply a hierarchical decomposition of media objects. Often there are two kinds of hierarchies: content hierarchy: illustrated above. coding hierarchy: based on data encoding
