Unit 4-2 Commonly Found Internet File Types

After completing this unit, you will be able to:

• Recognize the commonly found Internet file types.
• Understand how browsers launch different plug-ins and helper applications to play certain types of files.
• Explain why MIDI files occupy so much less file space than waveform audio files.
• Understand the concept of a markup language.
• Know the difference between the GIF and JPEG graphics formats.
• Understand why the audio/video interleave (AVI) file format was designed to give audio the priority when a computer does not have enough processing time to show all of the frames of a movie.
• Explain the difference between lossy and lossless compression methods.
• Understand how animated GIFs can bring a Web page to life.
• Explain the concept of JavaScript.
• Understand the purpose of Adobe’s Portable Document Format.
• Know the rule search engines use to decide whether to include or exclude active server pages (ASP) files from a search.
• Avoid the common pitfall of changing a filename extension when you rename a file.

Reading

Read chapter 12 of the Internet Literacy textbook to study the concepts covered by this unit.

Online Activities

• Plain text files are identified by the filename extension .txt. In computer jargon, plain text files are known as ASCII files. ASCII (pronounced askey) stands for American Standard Code for Information Interchange. If you want to learn how ASCII files work from a technical standpoint, follow the Interlit Web site links to ASCII. Otherwise, it will suffice to remember that ASCII files are plain text files.
• HTML stands for HyperText Markup Language. The markup specifies how the text will flow onto the screen depending on the size and shape of the window in which the file is viewed. You will learn more about HTML in the Web page creation tutorial in Part Five of this course. To visit the official Web site where the latest HTML specification is found, follow the Interlit Web site link to HTML.
• GIF stands for Graphics Interchange Format. Invented by CompuServe for use on computer networks, GIF is highly efficient. GIF files are limited to a palette of 256 colors, however; if you need more than 256 different colors in a picture, you should use the JPEG format (see below). If you want to learn how GIF compression works, follow the Interlit Web site links to GIF.
• JPEG (pronounced Jay-peg) stands for Joint Photographic Experts Group, which is the name of the international standards committee that created it. JPEG is intended to become a platform-independent graphics format. JPEG images can contain millions of colors. For more information, follow the Interlit Web site link to JPEG.
• On multimedia PCs, the most common waveform audio filename extension is .wav, which stands for waveform. Both Netscape Communicator and Microsoft Internet Explorer have built-in support for playing WAV files. For more information about the .wav file format, follow the Interlit Web site links to waveform audio.
• High-end workstations, such as Sun and NeXT, create audio files in the .au and .snd formats. These formats are essentially the same, except that .au files do not have file headers to specify different sampling rates and compression formats. For more detail, follow the Interlit Web site links to Sun audio format.
• Real-time audio streaming used in Internet radio broadcasts requires a special file format optimized for real-time transmission over the Internet. The RealAudio filename extensions are .ra and .ram, which stands for Real Audio Metafile. Real audio metafiles are text files that contain the Web address (URL) of a RealAudio file. For more information about the RealAudio file formats, follow the RealAudio links at the Interlit Web site.
• AIFF stands for Audio Interchange File Format. This is the file format used to create audio files on the Macintosh. AIFC is a compressed version; the C stands for compressed. For more information about the AIF file formats, follow the AIF links at the Interlit Web site.
• MIDI stands for Musical Instrument Digital Interface. MIDI is a music synthesizer file format that requires very little bandwidth to transmit, because the sound chip inside your multimedia PC does the work of generating the waveform you hear. There are some incredible archives of MIDI files that you can listen to at the Interlit Web site.
• The most common video format in the Windows world is Microsoft's Video for Windows, which uses the filename extension .avi. AVI stands for audio-video interleave, which describes a clever scheme in which audio frames are interleaved with the video. For detailed information, follow the links to Video for Windows at the Interlit Web site.
• One of Apple Computer Corporation's greatest gifts to the field of multimedia is the QuickTime audio-video format. Because of its cross-platform capabilities, QuickTime has become very popular on the Internet. The filename extensions of QuickTime movies are .qt and .mov. For the latest information, follow the QuickTime links at the Interlit Web site.
• MPEG is emerging as the digital video standard for the United States and most of the world. MPEG stands for Motion Picture Experts Group, the name of the ISO standards committee that created it. For detailed information on MPEG, follow the links to MPEG at the Interlit Web site.
• One of the greatest challenges on the Internet is to deliver to your PC full-motion video in an uninterrupted real-time data stream. First to market with a product that does that is Progressive Networks. The name of the product is RealVideo, and the filename extension is RM. RealVideo follows the industry-standard real-time streaming protocol (RTSP) that has been invented for streaming audio and video over the Internet. To read about this and other technical details, follow the links to the RealVideo Technical White Paper at the Interlit Web site.
• There is a huge amount of printed text that is not accessible on the Web yet. To provide a way to digitize printed text into a format that can be viewed on any computer platform, Adobe created the Portable Document Format, for which the filename extension is .pdf. To learn more about the PDF file format, and to see some examples of PDF files in action, follow the links to Adobe Acrobat and Portable Document Format at the Interlit Web site.
• Web pages presented via the HTML file format are two-dimensional displays of text and graphics. The Virtual Reality Modeling Language (VRML) extends the Web into a third dimension. To learn more about VRML, follow the VRML repository links at the Interlit Web site, where you will find the "Cyberspace" paper that led to the creation of the VRML file format.