视频点播

• Providing Video Films on Demand提供视频点播电影
• Local News and Weather Forecasting各地新闻天气预报
• Games, Music and Leisure游戏音乐与休闲
• Education and Remote Learning Facilities教育和远程教学设施
• Home Shopping and Other Consumer Services家居购物等消费服务
• Banking银行

Fig : An interactive user无花果:交互式用户 云南博客}N,RhO1R,a&p:Q
interface under development by BT正在开发的接口胜

2 : Video on Demand : a Brief Look2:视频点播:简看

Formats...格式: 云南博客*~|\eSJ-j
U&\
Prerecorded videos be digitally stored in a video server.录像带被储存在数码存储视频服务器. These videos are then transmitted in a coded, compressed format.这些录像带然后转发了编码,压缩格式. After the videos are ordered (either via interactive voice response or two-way remote control), they are decoded and decompressed by set-top converters in individual homes.录像后,下令(不论语音或经双向遥控)他们的减压、解码机顶变换器个人家园. In preliminary demonstrations, picture quality has been equal to standard VHS.在初步示范,画面品质水准已经相当于租借.

Functionality...功能:
X7Sn)\+U}L0The customer can call on a range of services.顾客可以要求一系列的服务. While watching movies, performing operations such as video selection, pause, rewinding etc. can be selected as if it were a video player.一边看电影,筛选录像等手术,稍停,复卷等可挑选球员就像是录象. These are processed by the set-top-box and sent to the local server.这些都是处理的机顶盒送到当地服务器. The local server processes the request if possible, otherwise it relays the request to a video archive server, much as a hierarchy system.本地服务器程序请求如有可能,否则转播录像馆请求服务器作为一个多层次体系.

Network..网络.. 云南博客A0T1kC}\!?
Video-on-Demand currently runs over cabled networks, the most widespread being the standard telephone line.视频点播目前经营超过拍到网络,最普遍的标准电话线. The difficulty in this, though, is the relatively low transmission speed of the telephone line.在这困难,虽然是比较低的电话线传输速度.

To overcome this shortfall, there are several viable networking standards, developed for multimedia transmission over the Internet as explained later.为克服这一不足,有几种可行的联网标准,制定对网上多媒体传输稍后解释.

We will now examine the roles of the set-top-box, video server storage, Media compression standards and Transmission protocols.我们现在的角色审视机顶盒、视频服务器存储、媒体压缩标准和传输协议. Following that, we shall see how these relate to VoD.接着,我们将看到如何把这些关乎点播.

3 : Into the Details..3:详谈..

3.1 : Set-Top Box310:机顶盒

3.2 : Video Server320:视频服务器

• Capacity to hold hundreds of Mbytes (or perhaps order of Terabytes) of digital information容量举行数百比特(或者字节顺序)数字信息
• Provide simultaneous access to several hundreds (or thousands) of subscribers on real-time, giving each one an appropriate bandwidth (usually in the order of 1.5-6 Mbps)同时提供查阅数百(或数千)用户对实时、让每一个合适的带宽(通常在1.5-6Mbps的顺序)
• Make economical use of resources by dynamically allocating programmes into different media such as Magnetic tape, optical W/R disks, hard disks, by considering the relative usage and level of interactivity supported.节约资源动态分配方案为不同媒体如磁带、钨光/住宅盘硬盘的使用情况和程度的相对考虑互动支持.

As the table 1 highlights, solid-state storage as RAM is prohibitively expensive.正如表1突出、固态存储器作为储存费用非常昂贵. On the other hand, cheap alternatives such as tapes limits the sessions per device and also impose difficulties in virtual VCR functioning.在另一方面,廉价替代品,如磁带设备,也限制了每节施加困难虚拟录像机运转.

There are several important considerations in designing a feasible video server:有几个重要的考虑,设计一套可行的视频服务器:

1. Hierarchical storage scheme分层存储计划
2. Scalable Architecture建筑规模
3. Storage Subsystem存储子系统
4. Expanded Storage扩展存储

Fig : A loosely coupled implementation of a Video storage system无花果:一个松散耦合实施录影存储系统 云南博客(gD%WG(\ orL

2.2. Scalable Architecture :可调整架构: 云南博客1{
S(cz:b'?;EXz
The server system should be expandable both in terms of the number of titles held and the number of subscribers.服务器系统应可扩展,无论在数量和用户人数职称举行. This can be achieved by incoorporating set of parallel data servers and a name server to store the location and access control information of the programmes, as shown in the figure.这可以通过incoorporating一整套并行数据服务器和名字服务器存放地点和访问控制信息的节目,数字显示. Thus any user request is served by first accessing the Name Server to locate the appropriate Data Server.因此要求任何用户接入服务的第一名字服务器找到合适的数据服务器.

3.3. Storage Subsystem :存储子系统:

Goe,sv0The storage subsystem consists of control units, disk/tape storage and access mechanism.仓库管理子系统组成单位,磁盘/磁带储存和使用机制.

There are several techniques to increase the performance by interleaving digital data of a programme on multiple disks:有几种技巧增加了表演节目交错多重数字数据光盘:

• Striping involves interleaving portions of disk blocks on multiple disks.交错带部分涉及磁盘块多盘. The aim here is to reduce the latency for block access by parallel reading of the complete block.这里的目的是要减少潜伏期座读完全进入平行块.

• Declustering , on the other hand, distributes blocks of files on several disks, thus allowing parallel block access from the same file and increasing the rate of the video stream.分布在另一方面,分发档案数块磁盘从而使并行块来自同一档案和接入速度的提高视频流.

• The overall performance can also be enhanced by replicating files among the servers by considering the demand for a programme, relative dispersion of subscribers and the access patterns (eg: time/day of peak access, average number of simultaneous viewers..)整体表现还可以增强复制在档案伺服器的需求考虑一个节目相对分散的用户接入方式(如:时间/天进入高峰期,平均观众人数同步..)

4.4. Expanded Storage (ES)扩展存储(权证) (ie. solid-state memory) containing RAM modules would be the best for storing programmes with the highest demands, as in theory, ES has infinite bandwidth ; and in practice the transfer rate is only limited by the system bus speed.(即固态存储器)单元将含有羊的最佳储存方案的最高要求,由于在理论上具有无限频宽权证;并在实践中转移率只有有限的系统总线速度.

3.3 : Audio/Video Standards330:音频/视频标准

Apple Quicktime苹果quicktime

Apple Quicktime is a motion picture compression standard which is currently used for video conferencing.quicktime是苹果影业压缩标准是目前用于视频会议. Quicktime provides constant play speed, but when transmission rates slow down, picture quality is compromised: the images blur, frame. skipping occurs, causing jerkiness.quicktime提供发挥速度不断,但当传输速率慢,画面质量是妥协:画面模糊,帧飞出去,造成jerkiness.

Quick-Time is being used for media-compression by several firms including BT, MGM and Bell Atlantic (US) .速效时间用于媒体的数家公司,包括压缩胜、装、大西洋贝尔(美国). Apple is working with a number of partners on the development of an interactive television set-top box, based on the PowerPC processor.苹果正与一些伙伴就发展互动电视机顶盒,基于采用PowerPC处理器. Apple is also developing a proprietry set-top-box based on PowerPC processor for Quick-Time compatibility.苹果还开发了proprietry机顶盒基于PowerPC处理器快读兼容性.

Motion Picture Experts Group (MPEG)电影专家小组(MPEG的)

MPEG is a group of people that meet under ISO (the International Standards Organization).MPEG的是一群人,在满足标准化(国际标准组织). They generate standards for digital video (sequences of images in time) and audio compression.它们产生的数字视频标准(时间序列图像)、音频压缩. MPEG works closely with many international standards bodies:MPEG的工作,并与许多国际标准组织:

• jointly with the ITU-TS for ATM Video Coding.同国际电信联盟期内的ATM视频编码.
• collaborates with representatives from EBU, ITU-RS, SMPTE, and the North American High Definition TV community.同来自联盟,国际电联遥感、光电、北美高清晰度电视.

MPEG video has a compression ratio of about 26:1 while that for audio goes up to 7:1.具有视频压缩比大约为26:1,而音频则上升到7:1.

Real time MPEG encoding (and decoding, of course) hardware exist, costing from US$10,000.实时的MPEG编码(解码,当然)硬件存在,从成本10,000美元. There are several MPEG decoding chips available since 1993, such as;有几个可用的MPEG解码芯片1993等;

• SGS-Thompson STi-3500 - The first MPEG-2 chip on marketsgs-汤普森性病-3500-第一MPEG-2的芯片市场
• LSI Logic L64112 successor - capable of 15Mbit throughputLSI的逻辑l64112继任能力15mbit吞吐量
• IBM Single-chip decoder (http://www.crs4.it/~luigi/MPEG/ibmchip. html)IBM公司的单解码芯片(http://www.crs4.it/~luigi/MPEG/ibmchip.html)

MPEG is currently being adapted to many applications:目前正在适应的MPEG许多应用:

• MPEG-2 video and audio will be soon used in DSB (Direct Satellite Broadcast) with Thomson's STi-3500 architecture in DirecTV in N. America.MPEG-2视频和音频将很快用于联合会(直接广播卫星)与汤姆森的性病-3500建筑DIRECTV号在美国国宝.

• The Cable Industry has more or less settled down for MPEG-2, but with conflicting options for audio standards.有线电视业或多或少安顿MPEG-2的,但随着冲突的备选音频标准. (Eg: Generl Instruments , US's lagrest cable TV set-top box manufacturer, has announced the Dolby AC-3 as thier future audio standard.)(例如:广义文书,我们的lagrest有线电视机顶盒制造商已经宣布杜比交-3作为他们未来的音频标准).

• The US Grand Aliance, a consortium for US terrestrial HDTV standard, has already agreed to use MPEG-2 Video and System Syntax.美国盛大aliance、财团美国高清晰度电视地面标准已同意使用MPEG-2视频和系统语法.

Comparison of Quicktime and MPEG compressions比较QuickTime和MPEG的compressions

Click here for Quick-Time点此快读 云南博客6f-j:M8O,Nk"Jc video clips from Speechless从无言短片 X IT$F'QK)s{0and Tankgirl .而tankgirl.		Click for an MPEG encoded点击#27encoded 'C-Q2Rl,f'JC?\0movie clip from Under Siege电影夹从围困

Caution : The movies are over 1 Mbyte in length.注意:电影中有超过1兆字节的长度. This may这可能 云南博客EEb*o&n&T{0d({j
take a considerable time in heavy traffic periods.需要一段相当长的时间,在繁忙的时期.

3.4 : Transmission Protocols340:传输协议

ISDN (Integrated Services Digital Network)isdn(综合服务数字网)

ISDN is a set of communications standards allowing a single wire or optical fiber to carry voice, digital network services and video.网路通讯标准是一套允许单一光纤丝或携带声音数字视频和网络服务. ISDN is intended to replace POTS (Plain Old Telephone System) and differs in the telephone company central switches, software and other equipment.ISDN的目的是取代盆(平原旧电话系统)和中央不同电话公司交换机,软件和其它设备. Its bandwidth standards range from 64 kps up to 2.0 Mbps.其标准从64光启带宽高达2.0兆字节. ISDN is the current affordable alternative to POTS and is avaliable readily in Australia, France, Japan and Singapore, with the UK somewhat behind and availability in the USA rather spotty.ISDN的负担是当前替代盆可随时在澳洲与法国、日本、新加坡、与英国比较落后,在美国获得相当参差不齐.

ADSL (Asymmetric Digital Subscriber Loop)ADSL(非对称数字用户环路)

ADSL has the advantage that it runs over the current twisted pair copper (POTS) phone lines addressing the problem with changing to coax/fiber: For example, in New Jersey, Telcos phone company installs new cabling up to 7% of their installed access line base per year, itself growing at about 3% annually.ADSL的优点,它已违反了现行的铜双绞线电话线(盆)与解决改变哄/光纤:例如,新泽西州电信电话公司安装新的布线达到7%的接入线路安装基地每年本身每年增长约3%. Hence, the net upgrade to overhaul the network at 4% annual would take 25 years, after Telcos reach top speed.因此,全面提升净网为4%,每年需25年后达到最高时速电信. ADSL presents the solution using POTS.使用ADSL的礼物解盆.

ATM (Asynchronous Transfer Mode)ATM(异步传输模式)

ATM is a current research hot topic.ATM网是目前研究的热门话题. It is a method for dynamic allocation of bandwidth using a fixed 53 byte packet (cell), known also as "fast packet".这是一种利用动态分配带宽固定53字节数据包(细胞)又称"快速分组".