But so what? Links are used everywhere!
Yes they are but if you look at these two you will see that the first is a link to an executable ".
exe" file and the second is a link to a JPEG ".jpg" file. You will also notice that the link to the ".exe" file opens a dialog to start downloading the file to your computer. The second link displays the JPEG file in your browser.Why do they do that? Neither file is a HTML document. Even the Executable file is not executed but downloaded.
The reason is based in the World Wide Web itself and how web content is delivered to your computer from a server. Many people tend to confuse the Internet with the World Wide Web. The Internet has been around for over 25 years as a means to connect computer systems together. Initially, the majority of information on the Internet was transferred as files and later through newsgroups and e-mail.
It was not until the invention of the World Wide Web by Tim
Berners-Lee in 1990, only 10 years ago, that Web Pages and Web Sites became possible. The WWW provides a protocol by which information can be located, transferred and processed. HTTP allows HTML web pages to be sent so that a Browser can receive and interpret the data. But the WWW is not restricted to HTML.A question I often receive asks how to add multi media files to a web site. In many instances this is very simple. A multi-media file can be transferred in exactly the same way as a HTML,
JPEG or GIF file. Simply create a HTTP link to the file and away you go. Try this 315 kb avi file: slogo.aviDid it work? For most of you it probably did but for a few of you it may not. The reason is that the WWW provides the framework by which files are transferred and processed but it does not provide the application to actually process the file. I am sure that most of you will understand that you need a Browser in order to view Web Pages. HTTP provides the mechanism to transfer the HTML file but it is the Browser that will interpret it. The same is true of the link to the above "
avi".Browsers include a lot of applications that many of us take for granted. It is Obvious that the browser will interpret the HTML and display the text. It will also display GIF, JPEG and many other image file formats. Audio files however, are not officially supported by all Browsers. Internet Explorer will recognize and process Wave and Midi files through the BGSOUND tag but Netscape will not. In order for Netscape to play audio it must use a 3rd party Plug-In or a Helper application. (A Plug-In works inside the Browser while a Helper Application is completely independent of the Browser). In either case, it is not Netscape that plays the audio but the 3rd party application.
When a multi-media file can be loaded and executed without any other information being provided, it is usually enough to simply provide a hyper-link to it as I did above. When you wish to provide more control over the multi media application, you will need to use a specialize tag such as BGSOUND, EMBED or OBJECT. These tags allow you to pass parameters to the Plug-In that can control many of its functions and operations. I will talk about these tags in more detail next week.
The bottom line here is that in order to play a Multi Media file, the viewer will need to have an appropriate application installed on their computer. Just because an AVI, MPEG, Flash or other file works on your computer don't assume that it will work for all your visitors. The general rule is if you are going to use Multi-Media files, you should also provide a link to a downloadable player and you should not automatically play the multi media file unless you have warned your visitor and given them a chance to either download the player or leave. Since Multi-Media files tend to be very large, you should also warn your visitors of the size of the files before they are downloaded.
So you have set up your multi media files, provided links and been courteous enough to inform your visitors of everything they need to know. Is that it? Not quite.
You cannot take if for granted that any multi media file type can be put on your server even if you do provide a player. The reason is that the Server and your Browser may not know what to do with the file.
Why not? If you think about it, it will become apparent. When you link to a HTML document the server knows that you want it transmitted to your Browser. If you access a CGI script however, the server will not transmit the file but will execute the script. When the browser does start to receive a stream of date from the server how does it know what to do with it? It may receive a stream of Image data followed by some HTML, a bit of
Javascript etc.
Your Browser will know how to process the data because the Server will add a MIME type to each block it sends to it. MIME is an acronym for Multipurpose Internet Mail Extension and is used to enable the Browser to identify the data it is receiving so that it can launch the appropriate program to process it.
For the system to work, it is consequently necessary for both the server and the visitors browser to understand the Mime type. Unfortunately this presents a problem since you as the Web Page author, probably do not have access to either your ISP's server or your visitors Browser.
Most ISP's I have dealt with are receptive to adding a new MIME type to their servers provided it is legitimate and does not conflict with any other MIME types. Setting a MIME type up for your visitors is more problematic especially for Helper
Apps which are not pre configured in most Browsers.For most software companies distributing Multi-Media applications over the Internet, this is a real challenge. Most web surfers are very reluctant to download and install additional applications on their computer unless they have a real desire to do so. Even well established applications such as Real Audio and Flash are not installed on a majority of end users computers.
As a Web Page author it is important to know which multi media additions to your Web Page will be generally supported and which ones may cause problems for many of your visitors. Does that nifty sound track or streaming video really add a lot to your web site or does it just server to drive away a lot of your visitors?
More Multi-Media next week.
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