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1、专业外语课程目标n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n讲授为主n偶尔通过录音、电影等形式来提高听力理解能力Part 1 Digital MediaText1:Multimedia An OverviewAdvances in distributed multimedia systems have begun to significantly affect the development of on-demand multimedia services.Researchers a
2、re 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.nMultimedia systems combine a variety of information sources,such as voice,graphics,animation,images,audio
3、,and full-motion video,into a wide range of three industries:computing,communication,and broadcasting.nResearch and development efforts in multimedia computing fall into two groups.nOne group centers its efforts on the stand-alone multimedia workstation and associated software systems and tools,such
4、 as music composition,computer-aided learning,and interactive video.nThe other combines multimedia computing with distributed systems.nThis offers even greater promise.Potential new applications based on distributed multimedia systems include multimedia information systems,collaboration and conferen
5、cing systems,on-demand multimedia services,and distance learning.nThe defining characteristic of multimedia systems is the incorporation of continuous media such as voice,video,and animation.nDistributed multimedia systems require continuous data transfer over relatively long periods of time,media s
6、ynchronization,very large storage,and special indexing and retrieval techniques adapted to multimedia data types.1.Technical DemandsnA 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 vi
7、deo 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 requires g
8、reat processing power to implement software codecs,multimedia file systems,and corresponding file formats.The architecture must provide high bus bandwidth and efficient I/O.nA multimedia operating system should support new data types,real-time scheduling,and fast-interrupt processing.Storage and mem
9、ory 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.nWe also need new object-oriented,user-friendly software development tools,as well as tools
10、for retrieval and data management-important for large,heterogeneous,networked and distributed multimedia systems.nResearchers are working within established computer areas to transform existing technologies,or develop new technologies,for multimedia.nThis research involves fast processors,high-speed
11、 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,par
12、allel processing methods,and complex architectures for distributed systems.2.Multimedia CompressionnAudio,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 compression fo
13、r 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,implemented
14、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 ratios,t
15、hough,and therefore are applied more often in image and video compression than lossless techniques.nWe can further divide the lossy techniques into prediction-,frequency-,and importance-based techniques.Predictive techniques predict subsequent values by observing previous values.nFrequency-oriented
16、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.nHybrid compression techniques combine several
17、 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.nWhen implementing a compression/decompression algorithm,the key question is how to par
18、tition between hardware and software in order to maximize performance and minimize cost.nMost implementations use specialized video processors and programmable digital signal processors.However,powerful RISC processors are making software-only solutions feasible.nWe can classify implementations of c
19、ompression 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 networkingnMany applications,such as video m
20、ail,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.nSuch applications might require broadcasting multimedia data to various remote locations or accessing large dep
21、ositories of multimedia sources.nTraditional 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.nTraditional networks do not suit multimedia.E
22、thernet provides only 10 Mbps,its access time is not bounded,and its latency and jitter are unpredictable.nToken-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.nAn FDDI network
23、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.nHowever,due to the high cost,FDDI networks are used primarily for backbon
24、e networks,rather than networks of workstation.nLess expensive alternatives include enhanced traditional networks.Fast Ethernet,for example,provides up to 100 Mbps bandwidth.Priority token ring is another system.nPresent optical network technology can support the Broadband Integrated Services Digita
25、l Network(B-ISDN)standard,expected to become the key network for multimedia applications.B-ISDN access can be basic or primary.nBasic 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 the US a
26、nd 30B+D in Europe.nProposed 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.nSTM provides fixed bandwidth channels,and therefore is not flexible enough to handle the different types of
27、traffic typical in multimedia applications.nOn 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.nATM can also increase the bandwidth efficiency by buffering and statistical
28、ly multiplexing bursty traffic at the expense of cell delay and loss.4.Multimedia systemsnAdvances in several technologies are making multimedia systems technically and economically feasible.nThese advances include powerful workstations,high-capacity storage devices,highspeed networks,advances in im
29、age and video processing,advances in audio processing,speech processing,and advanced still,video,audio,and speech compression algorithms.nA multimedia system consists of three key elements:multimedia hardware,operating system and graphical user interface,and multimedia software development and deliv
30、ery tools.nSince 1989,when the first multimedia systems were developed,it has been possible to differentiate the three generations of multimedia systems.nThe first generation,based on Intel 80386 and Motorola 68030 processors,is characterized by bitmapped images and animation,JPEG video compression
31、techniques,local area networks based on Ethernet and token ring,and hypermedia authoring tools.nThe 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 incorporat
32、e text,graphics,animation,and sound.nWe 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.nCompression
33、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.nThe authoring tools will integrate object-oriented multimedia into the operating system.5.A
34、pplicationsnMultimedia 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.nMultimedia mailing systems are more sophisticated than standard electronic mailin
35、g systems.They implement multiple applications,such as multimedia editing and voice mail,and require higher transmission rates than text-only system.nCollaborative work systems allow group members to discuss a problem and actually create something together.During a meeting,users can view,discuss,and
36、 modify multimedia documents.nMultimedia 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.nEach participant can send and
37、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.nMultimedia conferencing systems must provide a number of functions,such as
38、 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 nResearch and development in high-speed n
39、etworks will soon provide the bandwidth needed for distributed multimedia applications.Therefore,I envision tremendous growth in distributed multimedia systems and their applications.nAdvances in distributed multimedia systems have begun to significantly affect the development of on-demand multimedi
40、a services,such as interactive entertainment,video news distribution,video rental services,and digital multimedia libraries.nVarious companies realized that fiber optic networks,coupled with improved computing and compression techniques,would soon be capable of delivering digital movies.Over the pas
41、t year,a number of alliances have formed between entertainment,cable,phone,and computer companies,with the main focus on video-on-demand applications.nMany challenging problems remain to be researched and resolved for the further growth of multimedia systems.Multimedia applications make enormous dem
42、ands on computer hardware and software resources.Therefore,one of the ongoing demands is to develop more powerful multimedia workstations.nMultimedia workstations will also need multimedia operating systems(MMOSs)and advanced multimedia user interfaces.An MMOS should handle continuous media by provi
43、ding preemptive multitasking,easy expandability,format-independent data access,and support for real-time scheduling.nIt should be object-oriented and capable of synchronizing data to be instantly available,so the user interface must be highly sophisticated and intuitive.nIntegrating the user interfa
44、ce 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.nThe constant challenge is further refinement of high-spee
45、d,deterministic networks with low latency and low jitter,as well as research in new multimedia synchronization algorithms.New words and expressionsnaccess time 存取时间nalgorithm n.算法nasynchronous transfer mode(ATM)异步传输模式nbandwidth n.带宽nbrowsing n.浏览nchannel n.信道、通道ncodec n.编码译码器ncompression n.压缩ndiffer
46、ential pulse code modulation 差分脉码调制ndigital signal processor 数字信号处理nFourier transform 傅里叶变换nheterogeneous 不同种类的，杂散的nhuman-computer interface 人机接口nhybrid n.混合nhypermedia n.超媒体 nhypertext n.超文本ninteractive video 交互视频nisochronous 等时的njitter n.抖动，跳动nlatency n.等待时间nmultimedia file system 多媒体文件系统nnon-interactrve 非交互式的npartition n.划分nreal-time scheduling 实时调度nretrieval n.检索nspeech processing 语音处理nstand-alone multimedia workstation 独立多媒体工作站nstill image 静止图像nsynchronized mode 同步模式nsynchronous transfer mode(STM)同步传输模式ntext-to-speech conversion 文本语音变换ntoken ring 令牌环网ntransfer rate 传输速率nwavelet n.子波，小波