Web Programming Unleashed
by Antonio Miguel Ferreira
- Finding Out How VDOlive Works
- Installing a VDOlive Player
- Installing a VDOlive Server
- Creating Video Clips
- Linking Video on WWW Pages
- Watching Video Clips Over the Internet
VDOlive is a relatively new technology that supports both video
and audio broadcasting on the Internet or on other TCP/IP networks
such as intranets. VDOlive broadcasts resemble RealAudio audio
broadcasts; the main difference is that VDOlive adds a video signal
to the stream.
Traditionally, when a Web page contains a video, the user must download the whole file (MPEG, AVI, or any other format) and display it by using an external program running on his or her PC. Browser plug-ins and helper applications (built-in or external programs) enable downloading and automatic viewing. Unfortunately, downloading big video files (1MB to 10MB or more) can be a discouraging operation when you don't have a 56Kbps link (at least) to the Internet.
VDOlive technology is based on a scaleable video and audio compression algorithm and a protocol for transmissions of resulting files through the Internet. This technology enables you to view and download videos simultaneously; and the quality of the picture is proportional to the available Internet link bandwidth! The video file downloads and at the same time the player displays the part of the video that resides in the memory buffers. You do not have to download the entire video in order to watch it; you can see it while it is downloading. (The process is similar to listening to a radio station while it broadcasts its signal.) At the time of this writing, a VDOlive server could transmit only pre-prepared video files, but VDOnet Corp., the creator of VDOlive technology, is working to improve the technology to suit real-time compression and, consequently, real-time video broadcasting.
VDOlive is based on a client/server architecture, the client being the VDOlive player and the server being a VDOlive server (either the limited Personal Server version or the complete Video Server version). The client enables users to receive and view video clips, whereas the server transmits video over the Internet to users. Figure 31.1 summarizes the function of the VDOlive system.
Standard browsers cannot display real-time video and audio, so you must install a helper or plug-in application. This special-purpose program, which runs on the user's PC, interprets the video stream and displays it on a TV-like screen window. The plug-in to view VDOlive video clips is called VDOlive player. It is available for Windows and Macintosh platforms and works with most Web browsers.
On the server side, everything you need in addition to your Web server is a VDOlive server. This program runs in the background, listening to the default TCP port 7000, reads a file in VDO format from the local file system and transmits it over the Internet to a given client, using the UDP protocol. Two VDOlive servers are currently available: Personal Server and Video Server. The first is a limited test version, and the second is the complete program that can serve many video streams at the same time and scale up to different bandwidth connections.
You will have to capture video and audio sources (from VHS or Beta magnetic tapes) and then edit and compress them to the VDO format file, which is compatible with the AVI format. (In fact, the only good reason to have your own server on a Web site is to broadcast original video clips over the Internet.) You can use VDOlive Personal Tools, along with specialized video and audio capture hardware, to create your own video files. Other third-party tools, in particular tools for converting existing video formats (such as MPEG and QuickTime) to VDOlive format, are also available.
As for hardware, the VDOlive Web site (www.vdo.net) presents a list of video acquisition devices that can be used with VDOlive tools for content (video) creation.
You can find both VDOlive players and servers, as well as complete installation documentation and FAQs, on the VDOlive Web site at http://www.vdo.net/. Read on for an overview of the installation process for VDOlive products.
Installing a VDOlive player is easy. First, make sure you have the latest version of the software for your operating system. At the time of this writing, the current version is 2.0, either as a plug-in for the Netscape browser on Windows or Macintosh platforms or as a helper application for many other browsers. Video for Windows (a standard feature in Windows 95) optimizes the overall performance of VDOlive player, but isn't required.
After you download VDOlive player, run the executable file to start the installation process. If you are installing VDOlive player as a plug-in, you will be asked to name the folder in which Netscape 2.0 resides and to read the license agreement (please do). If you proceed, you must enter some personal information (name, e-mail address, and company) in order to customize your copy of the player. This information is logged in the VDOlive server's log files when you watch video clips over the Internet (be aware that companies that provide video clips may use the information concerning you for marketing or other business purposes).
Next, you must choose a folder in which to install the VDOlive player. A good choice is the plug-ins folder within the Netscape folder; if you plan to use VDOlive player as a helper application, choose any other folder. The setup program finishes by asking if you want to add icons to the Program Manager. Answer Yes, choose the program group for the icons, and the installation process will finish.
You are now able to connect to a VDOlive site and watch video clips over the Internet. A good starting point is, naturally, VDOlive's Web site. You can find lots of pointers to many other sites that deliver video content in VDOlive format.
If you experience problems, contact your Web site's administrators. They may have to open a UDP port on their Internet server so that the VDOlive server can send its video stream. You should configure your VDOlive player (Setup | Settings) to this specific UDP port.
VDOlive server can be installed in different hardware and software platforms: UNIX (all popular flavors) or Windows NT/95. Once again, make sure you have the latest version (as of this writing, it is version 2.0) of either the VDOlive Personal Server, which you can obtain from VDOlive's Web site, http://www.vdo.net/, or the VDOlive Video Server.
This section explains the installation process on a Linux server. (Installation on other UNIX systems is similar.) The VDOlive Personal Server is as easy to install as the VDOlive player is to install. After downloading the trial version of the server (about 1.4MB), you must run the executable (for example, vdoaout.exe) as root. You should read the license agreement carefully when it appears. The installation program creates a directory (/usr/local/vdosrv by default) for the vdosrv file (the server) and the VDOlive Personal Tools. By default, this directory also contains the server log files.
Finally, you can add a line to the file-/etc/rc.d/rc.local-(for other UNIX systems you should locate a similar file, the one that executes commands at system boot process) pointing to the vdosrv server, which will run in the background, listening to default TCP port 7000. (You can override this setting with the -d parameter.) If you do not want the server to run all the time, you can start it manually by running the binary file in the background. It is the best option if you just want to try the server for a while.
The VDOlive Personal Server version available at www.vdo.net has some limitations:
- The maximum number of streams it can serve at any time is two. Therefore, the maximum number of players you can connect to your server at any time is two.
- The maximum stream transmission rate scales up to 256Kbps, even if a greater link is available. This rate is adequate for normal dial-up connections to the Internet.
- The maximum video length that the Personal Server version can make available to users is 60 seconds.
- The server has an expiration date. After that you should upgrade to either a new Personal Server or, preferably, to the VDOlive Video Server, the complete version.
The license agreement of the VDOlive programs should give you any relevant information on using the server.
The VDOlive Personal Server is intended for testing purposes on home or small systems. If you plan to serve many clients over the Internet or to serve big video files, you should obtain the VDOlive Video Server, which can be adapted to as many video streams as you want.
Both versions of the server include software tools (VDOlive Personal Tools) that enable you to produce your own video clips in VDO format. The latest version is available only for Windows 95 or NT.
You can use one of the tools to capture analog video and audio from an analog source (VHS or Beta) and convert it to digital format. (For this conversion, you must also use a dedicated video capture card and Video for Windows.) Another "tool" enables users to compress previously prepared uncompressed videos to the VDOlive format, saving them as AVI files, which a VDOlive server can then transmit. There are also tools available to help you handle videos on MPEG or Quicktime formats.
A typical 160´120 video, with 15 frames per second and 24 bits per pixel, requires from 200KB to 1000KB per minute, depending on its compression rate.
A video link on a Web page is the URL of a VDO file; for example, http://www.foo.com/film.vdo. This VDO file is in fact a container of another URL (written in ASCII in the file), and the actual video file; for example, vdo://www.foo.com:7000/usr/src/videos/film.avi. The MIME type for the VDO files is video/vdo (the file mime.types-or similar file, containing all the MIME types supported by the Web server-on the Web server should include a line for this MIME type).
The actual video can be displayed on the browser's window, inside the Web page, or in an external VDOlive player window.
You can see the appearance of a Web page with the TV-like screen in Figure 31.2.
While you are surfing the Internet for videos, you may notice that most of the time you will find only demonstration videos, not real-life applications with a special purpose. The VDOlive technology is quite new, and its use is still evolving. In the future, we might be able to watch real-time videos (broadcasting) such as news programs over the Internet. Also, companies might consider video distribution over the Internet as an alternative to TV commercials or other presentations.
Although VDOlive works reasonably well over a 28.8Kbps link, at a maximum rate of 10 frames per second under ideal conditions, overall transmission quality (audio and video synchronization) is superior over an ISDN or T1 line-naturally-from which you can view 20 (or even more) frames per second. If you use a near site (to which your Internet provider has fast links), you will probably enjoy better video quality, because many times packets-and consequently frames-are lost over distant or saturated Internet links.
The transmission quality adapts to the quality of the receiving Internet connection. Although you can watch videos over a 28.8Kbps modem link (maximum rate of 10 frames per second), a 56Kbps, ISDN, or T1 link produces better quality.
The ideal transmission conditions depend not only on the available bandwidth, but also on the volume of Internet traffic over the various links traversed by the video stream and on the load on VDOlive servers. For example, viewing videos over a 14.4Kbps modem may be impossible unless conditions are ideal (that is, low traffic and low overload).
Also, video screens (the windows in which the video is displayed on your personal computer) are still limited to 160´120, 24 bits per pixel, which is big enough for viewing and enjoying the video clips but too small for viewing real applications (real-time broadcasting or film presentation clips, for example). This screen size limits the videos to only simple ones. Improvements on Internet links and in VDOlive technology should yield bigger and better video screens in the future.
The VDOlive site on the Internet is http://www.vdo.net/. You can find information concerning the VDOlive servers and player, as well as many links to other Internet sites delivering video content. VDOlive is a trademark of VDOnet Corporation, California (USA).