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1、专业外语,课程目标,掌握较多相关专业英语词汇和数字媒体的基本概念，为阅读专业文献和书籍打下坚实的基础，同时为在今后工作中解决与专业英语相关的问题提供必要的知识保证。,教学方法,讲授为主偶尔通过录音、电影等形式来提高听力理解能力,Part 1 Digital Media,Text1:Multimedia An Overview,Advances in distributed multimedia systems have begun to significantly affect the development of on-demand multimedia services.Researche
2、rs are working within established computer areas to transform existing technologies and develop new ones.The big picture shows multimedia as the merging of computing,communications,and broadcasting.,Multimedia systems combine a variety of information sources,such as voice,graphics,animation,images,a
3、udio,and full-motion video,into a wide range of three industries:computing,communication,and broadcasting.,Research and development efforts in multimedia computing fall into two groups.One group centers its efforts on the stand-alone multimedia workstation and associated software systems and tools,s
4、uch as music composition,computer-aided learning,and interactive video.The other combines multimedia computing with distributed systems.,This offers even greater promise.Potential new applications based on distributed multimedia systems include multimedia information systems,collaboration and confer
5、encing systems,on-demand multimedia services,and distance learning.,The defining characteristic of multimedia systems is the incorporation of continuous media such as voice,video,and animation.,Distributed multimedia systems require continuous data transfer over relatively long periods of time,media
6、 synchronization,very large storage,and special indexing and retrieval techniques adapted to multimedia data types.,1.Technical Demands,A multimedia system can either store audio and video information and use it later in an application such as training,or transmit it live in real time.Live audio and
7、 video can be interactive,such as multimedia conferencing,or noninteractive,as in TV broadcasting.Similarly,stored still images can be used in an interactive mode or in a noninteractive mode.,The complexity of multimedia applications stresses all the components of a computer system.Multimedia requir
8、es great processing power to implement software codecs,multimedia file systems,and corresponding file formats.The architecture must provide high bus bandwidth and efficient I/O.,A multimedia operating system should support new data types,real-time scheduling,and fast-interrupt processing.Storage and
9、 memory requirements include very high capacity,fast access times,and high transfer rates.New networks and protocols are necessary to provide the high bandwidth,low latency,and low jitter required for multimedia.,We also need new object-oriented,user-friendly software development tools,as well as to
10、ols for retrieval and data management-important for large,heterogeneous,networked and distributed multimedia systems.,Researchers are working within established computer areas to transform existing technologies,or develop new technologies,for multimedia.,This research involves fast processors,high-s
11、peed networks,large-capacity storage devices,new algorithms and data structures,video and audio compression algorithms,graphics systems,human-computer interfaces,real-time operating systems,object-oriented programming,information storage and retrieval,hypertext and hypermedia,languages for scripting
12、,parallel processing methods,and complex architectures for distributed systems.,2.Multimedia Compression,Audio,image,and video signals produce a vast amount of data.Compression techniques clearly play a crucial role in digital multimedia applications.Present multimedia systems require data compressi
13、on for three reasons:the large storage requirements of multimedia data,relatively slow storage devices that cannot play multimedia data in real time,and network bandwidth that does not allow real-time video data transmission.,Digital data compression relies on various computational algorithms,implem
14、ented either in software or hardware.We can classify compression techniques into lossless and lossy approaches.,Lossless techniques can recover the original representation perfectly.Lossy techniques recover the presentation with some loss of accuracy.The lossy techniques provide higher compression r
15、atios,though,and therefore are applied more often in image and video compression than lossless techniques.,We can further divide the lossy techniques into prediction-,frequency-,and importance-based techniques.Predictive techniques predict subsequent values by observing previous values.,Frequency-or
16、iented techniques apply the discrete cosine transform,related to fast Fourier transform.Importance-oriented techniques use other characteristics of images as the basis for compression;for example,the DVI technique employs color lookup tables and data filtering.,Hybrid compression techniques combine
17、several approaches,such as DCT and vector quantization or differential pulse code modulation.Various group have established standards for digital multimedia compression based on the existing JPEG,MPEG,and px64 standards.,When implementing a compression/decompression algorithm,the key question is how
18、 to partition between hardware and software in order to maximize performance and minimize cost.,Most implementations use specialized video processors and programmable digital signal processors.However,powerful RISC processors are making software-only solutions feasible.,We can classify implementatio
19、ns of compression algorithms into three categories:(1)a hardwired approach that maximizes performance,(2)a software solution that emphasizes flexibility with a general-purpose processor,and(3)a hybrid approach that users specialized video processors.,3.Multimedia networking,Many applications,such as
20、 video mail,video conferencing,and collaborative work systems,require networked multimedia.In these applications,the multimedia objects are stored at a server and played back at the clients sites.,Such applications might require broadcasting multimedia data to various remote locations or accessing l
21、arge depositories of multimedia sources.,Traditional LAN environments,in which data sources are locally available,cannot support access to remote multimedia data sources for a number of reasons.Table 2 contrasts traditional data transfer and multimedia transfer.,Traditional networks do not suit mult
22、imedia.Ethernet provides only 10 Mbps,its access time is not bounded,and its latency and jitter are unpredictable.,Token-ring networks provide 16 Mbps and are deterministic;from this point of view,they can handle multimedia.However,the predictable worst-case access latency can be very high.,An FDDI
23、network provides 100 Mbps bandwidth,sufficient for multimedia.In the synchronized mode,FDDI has low access latency and low jitter.FDDI also guarantees a bounded access delay and a predictable average bandwidth for synchronous traffic.,However,due to the high cost,FDDI networks are used primarily for
24、 backbone networks,rather than networks of workstation.,Less expensive alternatives include enhanced traditional networks.Fast Ethernet,for example,provides up to 100 Mbps bandwidth.Priority token ring is another system.,Present optical network technology can support the Broadband Integrated Service
25、s Digital Network(B-ISDN)standard,expected to become the key network for multimedia applications.B-ISDN access can be basic or primary.,Basic ISDN access supports 2B+D channels,where the transfer rate of a B channel is 64 Kbps,and that of a D channel is 16 Kbps.Primary ISDN access supports 23B+D in
26、the US and 30B+D in Europe.,Proposed B-ISDN networks are in either synchronous transfer mode(STM)or asynchronous transfer mode(ATM),to handle both constant and variable bit-rate traffic applications.,STM provides fixed bandwidth channels,and therefore is not flexible enough to handle the different t
27、ypes of traffic typical in multimedia applications.,On the other hand,ATM is suitable for multimedia traffic;it provides great flexibility in bandwidth allocation by assigning fixed length packets called cells,to virtual connection.,ATM can also increase the bandwidth efficiency by buffering and sta
28、tistically multiplexing bursty traffic at the expense of cell delay and loss.,4.Multimedia systems,Advances in several technologies are making multimedia systems technically and economically feasible.,These advances include powerful workstations,high-capacity storage devices,highspeed networks,advan
29、ces in image and video processing,advances in audio processing,speech processing,and advanced still,video,audio,and speech compression algorithms.,A multimedia system consists of three key elements:multimedia hardware,operating system and graphical user interface,and multimedia software development
30、and delivery tools.,Since 1989,when the first multimedia systems were developed,it has been possible to differentiate the three generations of multimedia systems.,The first generation,based on Intel 80386 and Motorola 68030 processors,is characterized by bitmapped images and animation,JPEG video com
31、pression techniques,local area networks based on Ethernet and token ring,and hypermedia authoring tools.,The second generation uses i80486 and MC68040 processors,moving and still images,16-bit audio,JPEG and MPEG-1 video compression,FDDI networks,and object-oriented,multimedia authoring tools that i
32、ncorporate text,graphics,animation,and sound.,We are presently at the transition stage from the second-to the third-generation systems,based on more powerful processors such as Pentium and PowerPC.The third generation will use full-motion,VCR-quality video,eventually moving to NTSC/PAL and HDTV.,Com
33、pression algorithms will include MPEG-2,-3,and-4,and perhaps the wavelets method now in the research stage.The system will use enhanced Ethernet,token ring,and FDDI network,as well as new isochronous and ATM networks.The authoring tools will integrate object-oriented multimedia into the operating sy
34、stem.,5.Applications,Multimedia systems suggest a wide variety of potential applications.Three important applications already in use are multimedia mailing systems,collaborative work systems,and multimedia conferencing systems.,Multimedia mailing systems are more sophisticated than standard electron
35、ic mailing systems.They implement multiple applications,such as multimedia editing and voice mail,and require higher transmission rates than text-only system.,Collaborative work systems allow group members to discuss a problem and actually create something together.During a meeting,users can view,di
36、scuss,and modify multimedia documents.,Multimedia conferencing systems enable a number of participants to exchange various multimedia information via voice and data networks.Each participant has a multimedia workstation,linked to the other workstations over high-speed networks.,Each participant can
37、send and receive video,audio,and data,and can perform certain collaborative activities.The multimedia conference uses the concept of the shared virtual workspace,which describes the part of the display replicated,at every workstation.,Multimedia conferencing systems must provide a number of function
38、s,such as multiple-call setup,conference status transmission,real-time control of audio and video,dynamic allocation of network resources,multiport data transfer,synchronization of shared workspace,and graceful degradation under fault conditions.,6.Research directions,Research and development in hig
39、h-speed networks will soon provide the bandwidth needed for distributed multimedia applications.Therefore,I envision tremendous growth in distributed multimedia systems and their applications.,Advances in distributed multimedia systems have begun to significantly affect the development of on-demand
40、multimedia services,such as interactive entertainment,video news distribution,video rental services,and digital multimedia libraries.,Various companies realized that fiber optic networks,coupled with improved computing and compression techniques,would soon be capable of delivering digital movies.Ove
41、r the past year,a number of alliances have formed between entertainment,cable,phone,and computer companies,with the main focus on video-on-demand applications.,Many challenging problems remain to be researched and resolved for the further growth of multimedia systems.Multimedia applications make eno
42、rmous demands on computer hardware and software resources.Therefore,one of the ongoing demands is to develop more powerful multimedia workstations.,Multimedia workstations will also need multimedia operating systems(MMOSs)and advanced multimedia user interfaces.An MMOS should handle continuous media
43、 by providing preemptive multitasking,easy expandability,format-independent data access,and support for real-time scheduling.,It should be object-oriented and capable of synchronizing data to be instantly available,so the user interface must be highly sophisticated and intuitive.,Integrating the use
44、r interface at the operating system level could eliminate many problems for application software developers.Other research challenges include developing new real-time compression algorithms,large storage devices,and multimedia data management systems.,The constant challenge is further refinement of
45、high-speed,deterministic networks with low latency and low jitter,as well as research in new multimedia synchronization algorithms.,New words and expressions,access time 存取时间algorithm n.算法asynchronous transfer mode(ATM)异步传输模式bandwidth n.带宽browsing n.浏览channel n.信道、通道codec n.编码译码器compression n.压缩diff
46、erential pulse code modulation 差分脉码调制digital signal processor 数字信号处理Fourier transform 傅里叶变换heterogeneous 不同种类的，杂散的,human-computer interface 人机接口hybrid n.混合hypermedia n.超媒体 hypertext n.超文本interactive video 交互视频isochronous 等时的jitter n.抖动，跳动latency n.等待时间multimedia file system 多媒体文件系统non-interactrve 非交互式的partition n.划分real-time scheduling 实时调度,retrieval n.检索speech processing 语音处理stand-alone multimedia workstation 独立多媒体工作站still image 静止图像synchronized mode 同步模式synchronous transfer mode(STM)同步传输模式text-to-speech conversion 文本语音变换token ring 令牌环网transfer rate 传输速率wavelet n.子波，小波,
