All About Multimedia
All About MultimediaWhat is 'multimedia'? what does the term most often refer to on the Web?As the term implies, "multimedia" literally involves using more than one type of media--usually text, graphics, animation and sound--to produce an object. Traditional "static" Web pages, therefore, could be considered multimedia, since they usually incorporate both text and graphics. However, the term multimedia is most often used in Web parlance to refer to the inclusion of audio, video and/or animation in a Web page. Recently, the advent of new Web multimedia standards such as Shockwave and VRML have expanded the meaning of the term even further. In order to keep the scope manageable, this FAQ focuses primarily on audio and video. The topic of animation will be covered in a separate, upcoming FAQ in Web Developer's "Graphics and Design" section. What are the most common audio and video file types on the Web? What are the pros and cons of each? The most commonly used audio formats on the Web are the AU (Audio Format), WAV (Waveform Audio) and AIFF (Audio Interchange File Format) file types. In brief, the formats break down like this:
The most common video formats on the Web are QuickTime (MOV), MPEG (Moving Picture Expert Group), and AVI (Audio Video Interleave). A similar breakdown of these formats follows:
For a more in-depth analysis of the various audio and video formats, see the "Fun with Formats" section in Does Multimedia Have a Dark Side? and Putting Video on Your Web Site: The Basics. What is 'streaming' audio and video? What are the most popular streaming formats? Many of the newest multimedia formats employ a process called data streaming. This method of delivery allows users to play audio and video files before they are completely downloaded. Usually streaming works by downloading an initial portion of the file, known as a buffer, into the user's viewer or player. This application then begins playback of the file while the remainder continues to "fill in." The buffer, as the name suggests, allows for continuous playback of the audio or video by compensating for any delays in the transmission of the rest of the file--at least in theory. Most of the streaming multimedia formats are proprietary, requiring special servers for encoding and transmission. Some of the most commonly used streaming audio formats are Progressive Networks' RealAudio (RA), and Xing Technology Corp's XingMPEG. More recently, Macromedia also made its voice heard in this market with the introduction of streaming audio for the popular Shockwave plug-in. The following table offers a quick glance at the specs on these file types:
The most common streaming video formats include XingMPEG video and VDOnet (VDO) file types. However, streaming video is a hot market, and the technology is advancing rapidly. Recently, a number of new streaming technologies and formats--primarily those designed to work within Netscape plug-ins--have entered the scene. These include Digigami's CineWeb, a non-proprietary codec that enables WAV, MPEG, AVI and QT streaming; and Vivo Software's VivoActive (.VIV) format, which compresses AVI video as much as 200:1. Other Netscape plug-ins, such as ClearFusion (aka CoolFusion), allow users to stream standard AVI and MPEG files automatically. So you might want to keep them in mind when choosing a format.
For a more in-depth analysis of the various audio and video streaming formats, see the "Fun with Formats" section in Web Developer®'s Does Multimedia Have a Dark Side? How do I create my own audio and video files? What software is available to produce A/V for the Web? For a great intro to producing video for the Web, check out Web Developer's Putting Video on Your Web Site: The Basics. This tutorial takes you through all the steps involved in Web video, from shooting and capturing the original source to linking the file to your Web page. Basically, producing video for your Web page involves two steps: digitizing and editing. There are both hardware- and software-based solutions for digitizing. Hardware-based video capture boards, commonly used for MPEG and AVI video, are usually expensive (often $4,000 and up). For an extensive list of MPEG hardware companies, see MPEG.org's MPEG-related Boards and Systems Manufacturers and Visible Light's MPEG Products Mall. These two sites also provide links to a number of software-based encoders for video production, which are often less-expensive alternatives to hardware boards and systems. QuickTime video hardware, on the other hand, is usually much lessexpensive than similar products for MPEG and AVI. And many Macintosh systems have on-board A/V hardware already built in, so that all you have to do is plug in a video source. For more info on QuickTime video production, see Apple's Developer Info and the QuickTime FAQ, which also contains software and resources sections. Where streaming video is concerned, most of the vendors listed in the table above provide specs and pricing info about their proprietary encoders on their Web sites. Once the video file is digitized, it's time to edit. Some of the top names in this category are Adobe's Premiere and After Effectsand Macromedia's Director. With the final product complete, the file can be uploaded to your server and linked from your Web site. For more on this final step, see How do I incorporate audio and video files into my Web pages? Creating audio files for the Web is a process similar to producing video, except most audio formats do not require special hardware devices to capture the original source. Often the audio source can be saved directly into your authoring/editing program. Even better news, some of the best digital audio editors are shareware, including Adobe Audition and GoldWave for Microsoft Windows. For more sophisticated users, commercial products such as Macromedia's SoundEdit 16, digidesign's Pro Tools or Sonic Foundry's Sound Forge should do the trick. Again, the streaming audio vendors' sites listed in the table above provide information about their proprietary audio encoders. How do I incorporate audio and video files into my Web pages?
Embedding A/V files is a more seamless method of integration, the drawback being that it only works with Netscape plug-ins. The <EMBED> tag uses the same parameters as the <IMAGE> tag, including SRC, HEIGHT and WIDTH. Additional, plug-in specific parameters can also be used, so that a typical embed command line might look like this:<EMBED SRC="MyMovie.mov", WIDTH=150, HEIGHT=250 CONTROLS=TRUE>See Netscape's Embed Tag Syntax for more info on embedding. The final option, client pull, is a less user-friendly alternative, primarily because it automatically downloads a specific file whether the viewer wants it or not. Client pull is achieved using a <META> tag line, such as:<META HTTP-EQUIV="Refresh" CONTENT="1; URL=myvideo.mov">< P> This command tells the user's browser to load a file (myvideo.mov) after an allotted amount of time has passed--in this case, 1 second, as specified in the CONTENT="1;" parameter. Another drawback of client pull is that the file will be reloaded each time the page is revisited, unless all the links from within the site refer to a version of the page without the client pull command. For more on client pull and its use in this manner, see Netscape's An Exploration of Dynamic Documents and Project Cool's Automatic Sound Files.Sampling frequency? Frame rate? 16-bit? Can you help me out with some of this A/V jargon? Lost in the maze of multimedia terms? Here's a quick reference guide to some of the most commonly used terms and acronyms:
Because audio and video files are usually large, adding these data types to your Web page or site can create two general problems: 1) they consume lots of storage space, typically a problem if you are leasing server space from an ISP or if you include a large number of files in your site; and 2) they consume lots of available bandwidth. Bandwidth consumption is a problem shared by those who lease server space as well as those who maintain their own server. If you are renting space, most ISPs only allow a certain amount of data--commonly 200-300 MB a day--to be transferred in a given period of time. A 2 MB QuickTime movie would only need 100 hits, therefore, to equal your daily quota. Bandwidth problems take on a whole different dimension if you run your own server. A server's connection to the Internet, often referred to as a "data pipe," can only handle so much data at once. This amount, typically equal to or less than the total capacity of the data pipe (e.g., 128 Kbps for an ISDN line, 1.56 Mbps for a T1 connection), is the server's available bandwidth. Because conventional multimedia files are transferred at as fast a rate as possible by the server (often called "bursty" transmission), they will consume as much of the available bandwidth as they can during transfer. And the files often take as much as 20-30 minutes to serve, so that both bandwidth and the server connection are tied up for the duration. Serve a large number of bulky mu ltimedia files, and both your server and your data pipe may quickly become "clogged." For a closer look at the server and bandwidth problems associated with multimedia, including a number of solutions for these downsides, see Does Multimedia Have a Dark Side? in the September/October issue of Web Developer. Sources and Resources for further multimedia exploration.
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