外文翻译----视频会议通过TCPIP协议在个人电脑上的实现

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1、视频会议通过TCP / IP协议在个人电脑上的实现by John F. McGowan, Ph.D.Desktop Video Expert CenterApril 24, 1997总体简介目前，视频会议系统通过TCP / IP协议的局域网和广域网在个人电脑上大量的安装和配置仍具有许多挑战。除了视频会议应用程序之外，还有视频会议系统的使用和在个人计算机之内频繁地修改如下五个子系统等挑战。 视频显示 视频采集 音频输出 音频输入 TCP/IP网络（包括网卡和TCP/IP的软件）每个子系统因本身就是较为复杂的。 因此，在视频会议系统的设施和配置期间，问题可能会发生系统的任何地方。 此外，程序又必须

2、在用户端安装，而在大多数个人计算机上，视频会议系统硬件和软件并不是标准的。通常来讲，不同的个人计算机上的软硬件导致在每台个人计算机安装的硬件和软件变化极大。即使一个经验丰富的安装高手在一台特殊用户的个人计算机上也可能遇到陌生的情况。所有版本的Windows- Windows3.1, Windows for Workgroups 3.1, Windows 95,Windows的即将发布的“Memphis”,以及WindowsNT都是建立在一个有处理系统部件和vendor-supplied设备驱动程序的复杂的系统之上的。一些设备驱动程序实际上是通过硬件设备实现,如视频显示卡,视频采集板、声卡、网卡

3、等。其他的设备驱动程序与硬件设备驱动性能有很多共同之处,但除TCP / IP协议的实施和具有系统特征的软件之外。设备驱动程序是非常强大的,因为在所有版本的Windows系统中他们在接入硬体和软件上都处在一个特权水平上。即使是在Windows 95,Windows 3.1中,系统仍允许多个应用程序占用操作系统的内存或其他的应用程序的内存。设备驱动操作的特权级别就意味着驱动比一个应用程序造成更为严重的损害。例如，难以言喻的奇怪的系统崩溃以及以及设备间冲突事故。此外，大多数的系统配置和安装问题都和驱动有关。尽管在此领域中将会遇到很多的问题不可能被预期,本文将会给出通过TCP / IP的网络实现的个人

4、电脑上的视频会议系统的有关整个安装和配置问题的一个概述。视频显示 视频会议系统的重点在于个人计算机的视频显示：视频适配器和视频驱动程序。视频显示驱动程序可以包含细微的错误，这将导致与应用程序发生冲突其中也包括与视频会议的应用程序发生冲突，造成包括一般保护错误和在屏幕上更新等问题在内的许多问题。一般来说，要确保视频卡具有的是最新驱动程序。大部分主流的视频卡和视频芯片供应商都会在其网站和FTP站点提供相应产品的驱动程序。对于部分用户有可能使用特殊显示卡驱动而不是一般的视频芯片驱动程序的情况，用户应向芯片制造商获取相应的驱动程序。例如，对于钻石系列的多媒体视频卡，无论是钻石显卡还是S3显卡，其供应商

5、在生产钻石系列芯片时都提供了相应的驱动程序。在钻石系列中，同S3相比大大增强了钻石显卡的驱动程序。一个错误的视频显示驱动程序在个人电脑上引起问题的情况通常是非常不明显的。视频会议所采用的数字视频标准是工作在YCrCb颜色空间而不是视频卡和显示器所采用的RGB色彩空间。例如H.261和H.263标准等。最新一代的视频芯片提供硬件色彩空间转换的功能。该芯片提供了将视频从YCrCb颜色空间（亮度，颜色的差异）转换为RGB的颜色空间的视频硬件解码，这大大提高了视频的播放速率。此外现在许多厂商的芯片都提供了硬件加速的图像缩放功能。安装具有这些具有先进的功能的视频卡的需要或愿望可能将会出现。 在Windo

6、ws95系统下，彩色空间的转换和图像的缩放功能是通过DirectDraw来访问API的。DirectDraw 的HAL（硬件抽象层）提供了实际设备的驱动程序。而在Windows 3.1系统下，标准的图形设备接口（GDI）并不提供硬件色彩空间转换或对图像缩放功能的支持。对于在Windows3.1系统下视频卡的标准设备驱动程序是GDI设备的驱动程序。著名芯片制造厂商英特尔公司定义了一个名叫DCI的标准，即显示控制接口的标准，支持诸如硬件色彩空间转换和图像缩放等高级功能。在Windows95系统下，视频卡必须安装正确的DirectDraw设备驱动程序以用来支持访问硬件来实现视频色彩空间转换和图像缩放

7、功能。在Windows3.1或Windows for Workgroups3.11系统下，一个DCI的驱动程序必须被安装以用来支持这些功能的实现。应用程序使用的GDI调用不能访问一般的硬件加速功能。因此，视频会议系统的应用程序必须适当的支持DirectDraw或DCI驱动。 视频会议系统应用程序通常含有一个文档，自述文件，等用来列出已知的视频显示硬件和驱动程序的冲突或问题。 视频显示应处理的问题 重新启动. 检查IRQ或其他资源冲突. 用显卡检查视频会议系统的错误记录文档. 确保有正确或者最新的显卡适配器驱动. 用Windows系统的控制面板重装显卡驱动. 使用显卡安装程序重新安装显卡驱动.

8、在Windows3.1下，通过编辑SYSTEM.INI中手动安装驱动程序（请备份 原始System.ini） 安装新的或不同的显卡.视频采集视频会议系统需要一个视频采集系统。一个视频采集系统包括一台摄像机，通常是NTSC或PAL复合视频相机，要么是ISA总线或PCI总线采集卡。通常，这些都不是预先安装在个人电脑上的。因此，对于个人电脑上的视频会议系统的安装，几乎总是要涉及一个视频采集卡和摄像头的安装。通常，视频采集硬件提供了视频会议应用程序。安装一个视频采集卡需要打开电脑机箱并将视频卡插入电脑中现有的ISA或PCI插槽。插口可能会出现问题，在那里的视频卡虽然是插在插槽中，但有可能会出现卡和卡槽

9、接触不完善或折断的状况。在这种情况下，软件将报告无法找到的视频采集卡或可能会发生其他状况。 视频采集卡通常是复合视频输入或复合视频输入加上S-Video输入。相机必须和此输入相连接。在某些情况下，即使是有电缆的接入也会出现不完美的电气连接出现。在这种情况下，安装程序必须处理的等待电缆的连接，直到一个工作建立为止。一些ISA视频采集卡要求在其芯片上通过跳线来选择IRQ的中断，虽然这种情况变得越来越少见但仍有出现。其他ISA视频采集卡仅通过软件进行设置就可以。而兼容即插即用的ISA和PCI视频采集卡有时会遇到资源冲突，这是由于即插即型卡设计实现的缺陷所造成的。 视频采集是通过VFW驱动程序来进行处

10、理的。在Windows 3.1和Windows for Workgroups系统下所提供的最新的16位的VFW程序是VFW1.1e版本。而在Windows95系统中提供了一个带有视频压缩功能的32位的VFW版本，此版本和VFW1.1e版还有一些未知的差异和联系，Windows95系统中所提供的这个版本的VFW已经具有视频采集的功能了。基于Windows 95 OEM服务版本2（OSR2）的ActiveMovie1.0，可以在Windows95的早期版本中安装，但它不提供任何对视频拍摄的支持。视频采集卡的软件安装过程中应安装VFW视频采集驱动程序。此驱动是有如下行定义的：MSVIDEO=xxxx

11、.drv在 Microsoft Windows SYSTEM.INI 文件中进行驱动选择。视频显示应处理的问题 重新启动. 检查IRQ或者其他资源是否冲突. 检查视频采集摄像头和网线连接.若有电气连接故障微调网线. 检查视频采集卡是否在主板上插装好. 用显卡检查视频会议系统的错误记录文档. 确保有正确或者最新的显卡适配器驱动. 用Windows系统的控制面板重装显卡驱动. 使用显卡安装程序重新安装显卡驱动. 在Windows3.1下，通过编辑SYSTEM.INI中手动安装驱动程序（请备份 原始System.ini） 安装新的或不同的显卡.视频会议的应用程序视频会议系统的客户端安装视频会议系统的

12、第一步都来自于应用程序的安装。这些通常是InstallShield或其它商业公司提供的安装程序。安装程序将安装包括所有应用的软件组件。安装程序经常也会伴随着安装视频会议系统所需的视频捕获卡和声卡。不幸的是，安装程序有时会安装失败。如果怀疑程序安装的有问题，请先卸载视频会议系统的程序，然后重新运行安装程序进行安装。在绝大多数情况下，这样操作都会有所帮助。 总结 视频会议系统通过TCP/ IP网络在个人电脑上的实现可能会涉及大量的个人电脑和网络的安装和配置。不幸的是，在个人电脑上安装和配置系统的硬件和软件是很复杂一件事。但在个人电脑上安装和配置系统的硬件和软件也不是像研究火箭科学那样艰难。它需要有

13、很多的步骤来去实现，特别是对于像视频会议系统这样复杂的产品。单独拿出每一步来说都很简单，但很多简单的步骤组合在一起，导致了一个相当复杂的过程。技术支持人员或用户必须避免被繁杂的步骤和频频出现的各种奇怪的问题所吓倒，哪怕问题是出现在Windows系统上的安装问题。 Videoconferencing on Personal Computers with TCP/IPby John F. McGowan, Ph.D.Desktop Video Expert CenterApril 24, 1997IntroductionVideoconferencing systems for PCs over

14、TCP/IP Local Area Networks and Wide Area Networks present substantial installation and configuration challenges. In addition to the videoconferencing applications, a videoconferencing system uses and frequently modifies five subsystems within a personal computer: Video Display Video Capture Audio Ou

15、tput Audio Input TCP/IP Network (both Network Interface Card and TCP/IP software)Each subsystem is complex in its own right. Thus, problems will likely occur somewhere during the installation and configuration of a videoconferencing system. As yet, videoconferencing hardware and software is not stan

16、dard on most PCs. Installation must occur at the user site. Generally, PCs vary significantly with different hardware and software installed on each PC. Even an experienced installer can encounter a new situation on a particular users PC.All versions of Windows - Windows 3.1, Windows for Workgroups

17、3.11, Windows 95, theupcoming “Memphis”, and Windows NT are built on a complex system of operating system components and vendor-supplied device drivers. Some device drivers manage actual hardware devices such as video display adapters, video capture boards, sound cards, and network interface cards.

18、Other device drivers share many properties with the hardware device drivers but implement TCP/IP protocols and other software features of the system.Device drivers are extremely powerful as they access the hardware and software at a privilegedlevel in all versions of Windows. Even in Windows 3.1 and

19、 Windows 95, which can allow applications to overwrite memory within the operating system or other applications, device drivers operate at a privileged level which allows the drivers to do even more damage than an application. Because of this device drivers can cause severe problems, inexplicable cr

20、ashes, and strange conflicts between devices. Most configuration and installation problems involve the device drivers.While it is impossible to anticipate the many situations that will be encountered in the field, this document provides an overview of the installation and configuration issues for vi

21、deoconferencing systems on PCs over TCP/IP networks.Video DisplayVideoconferencing systems make heavy use of the PCs video display: video adapter card and video drivers.Video display drivers can contain subtle bugs that can conflict with applications, including the videoconferencing applications, ca

22、using many problems including general protection faults and updating problems on the screen. In general, make sure to have the latest drivers for a video card. Most major video card and video chip vendors provide drivers on their Web sites and ftp sites. Use the video card drivers rather than generi

23、c video chip drivers where possible. For example, for Diamond Multimedia video cards, both Diamond and S3, the manufacturer of the video chips used in the Diamond Multimedia video cards, provide video drivers. Diamond has substantially enhanced the drivers for Diamond cards over the drivers provided

24、 by S3.It can be very unclear that a faulty display driver is the cause of a problem in a PC.The digital video standards used in videoconferencing such as H.261 and H.263 work in theYCrCb color space rather than the RGB color space used by video cards and monitors. The latestgenerations of video chi

25、ps provide hardware color space conversion. The chip converts the decoded video from the YCrCb (luminance-color difference) video into RGB in hardware, providing a substantial speedup. Many chips provide hardware accelerated scaling of images. The need or desire to install a video card with these ad

26、vanced features may arise.Under Windows 95, color space conversion and scaling are accessed through the DirectDrawAPI. The DirectDraw HAL (Hardware Abstraction Layer) provides the actual device driver. UnderWindows 3.1, the standard Graphic Device Interface (GDI) provides no support for hardware col

27、or space conversion or scaling. The standard device drivers for video cards under Windows 3.1 are GDI device drivers. Intel defined a standard called DCI, Display Control Interface, that supports advanced features such as hardware color space conversion and scaling. Under Windows 95, the correct Dir

28、ectDraw device driver for a video card must be installed to access the hardware color space conversion and scaling features. Under Windows 3.1 or Windows for Workgroups 3.11, a DCI driver must be installed to access these features. The videoconferencing application must support DirectDraw or DCI as

29、appropriate. An application that uses the GDI calls cannot access the hardware acceleration features in general.Videoconferencing applications often include documentation, readme files, and so forth that list known conflicts or problems with video display hardware and drivers.Things To Do for Video

30、Display Problems Reboot. Check for IRQ or other resource conflict. Check the videoconferencing system documentation for notes on problems with the video card. Make sure that you have the correct or latest version of the video display adapter device driver. Reinstall the video card using the Windows

31、Control Panel. Reinstall the video card using the video cards installation program. On Windows 3.1, manually install the drivers by editing SYSTEM.INI (make backup of original SYSTEM.INI) Install a new or different video card.Video CaptureVideoconferencing systems require a video capture system. A v

32、ideo capture system includes a video camera, typically an NTSC or PAL composite video camera, and a video capture card, either an ISA bus or PCI bus capture card. Usually, these are not provided pre-installed on the PC. Thus, installation of a videoconferencing system on a PC almost always involves

33、installation of a video capture card and camera. Usually, the video capture hardware is provided with the video conferencing applications.Installing a video capture card requires opening the PC case and inserting the card in anavailable ISA or PCI slot as available. Seating problems may occur, where

34、 the card appears to be seated in the slot but the electrical contact is imperfect or broken. In this case, the software will report a failure to find the video capture card, or other symptoms may occur.The video capture card usually has either a composite video input or a composite and an S-Video i

35、nput. The camera must be attached to this input. In some cases, the electrical connection will be imperfect even though the cables appear plugged in. In these cases, the installer must manipulate the cables until a working connection is established.Some ISA video capture cards require selection of t

36、he IRQ interrupts through jumpers on the ISA board, although this is becoming less common. Other ISA cards may be configured through software. Plug and Play compliant ISA and PCI cards may sometimes experience resource conflicts due to bugs in the Plug and Play implementations.Video capture is handl

37、ed through Video for Windows drivers. The most recent version of the 16 bit Video for Windows for Windows 3.1 and Windows for Workgroups is Video for Windows 1.1e. A version of Video for Windows with 32 bit video compressors and unknown other differences from Video for Windows 1.1e ships with Window

38、s 95. This Video for Windows (95) provides the video capture functions in Windows 95. ActiveMovie 1.0, which ships with Windows 95 OEM Service Release 2 (OSR2) and can be installed on earlier releases of Windows 95, does not provide any support for video capture. The video capture card installation

39、software should install a Video for Windows video capture driver. This driver is identified by the line:MSVIDEO=xxxx.drvin the drivers section of the Microsoft Windows SYSTEM.INI file.Things To Do for Video Capture Problems Reboot. Check for IRQ or other resource conflict. Check the cables connectin

40、g the camera to the video capture card. Jiggle and adjust the cables in case there is a faulty electrical connection. Check that the video capture card is properly seated in its slot on the motherboard. Check the videoconferencing system documentation for notes on problems with the video capture car

41、d. Make sure that you have the correct or latest version of the video display adapter device driver. Reinstall the video card using the Windows Control Panel. Reinstall the video card using the video cards installation program. On Windows 3.1, manually install the drivers by editing SYSTEM.INI (make

42、 backup of original SYSTEM.INI) Install a new or different video card.Videoconference ApplicationVideoconferencing ClientsVideoconferencing systems invariably come with installation or setup programs. These are often InstallShield or another commercial installation program. The setup program will in

43、stall all software components including applications. The setup program frequently installs video capture and sound boards that come with the videoconferencing system.Unfortunately, setup programs sometimes fail. When in doubt, uninstall the videoconferencing system and rerun the setup program. In a

44、 surprising number of cases, this will help.ConclusionPC Videoconferencing systems over TCP/IP networks can involve extensive PC and networkinstallation and configuration. Unfortunately, installation and configuration of hardware and software on PCs can be complicated. On the positive side, installa

45、tion and configuration of hardware and software on PCs is not rocket science. There are a lot of steps, especially for a complex system like a videoconferencing product. Individually, the steps are simple, but many simple steps leads to a complex process. Support personnel or users must avoid being intimidated by either the number of steps or the frequently bizarre symptoms of installation problems on Windows.