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12C H A P T E R Commonly Found Internet

File Types

When you use an Internet search engine to find something, the information is almost always returned in the form of a file. The way in which the file is organized is known as its format.

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Objectives:

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

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Objectives:

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.

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Objectives:

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. Avoid the common pitfall of changing a

filename extension when you rename a file.

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Text Formats

Plain text means just that—the text and nothing but the text.

There are three families of text formats: Plain text (TXT) HTML (Hypertext) Word processor files

DOC (Microsoft Word)WPD (WordPerfect)

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HTML

How a HTML file appears when viewed with a browser.How a HTML file appears when viewed with a text editor.

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Image Formats

The computer industry has produced so many graphics formats (more than 30 at last count) that there is no true standard across the industry.

On the Web, however, there are only two file formats that every Web browser can be guaranteed to support: GIF and JPEG.

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Image Formats

.bmp Windows bitmap. The .bmp file is the most efficient format to use with Windows.

.gif Graphics Interchange Format. Invented by CompuServe for use on computer networks, GIF is the most prevalent graphics format for images on the World Wide Web.

.pcdKodak’s Photo CD graphics file format; contains five different sizes of each picture, from “wallet” size to “poster” size.

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Image Formats

.jpg or .jpeg JPEG image, named for the standards committee that formed it: Joint Photographic Experts Group. Intended to become a platform-independent graphics format.

.pictMacintosh graphics format. .pngPortable Network Graphics format.

Pronounced ping, .png is the patent and license-free format approved by the W3C (World Wide Web Consortium) to replace the patented GIF format.

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Image Formats

.tga Truevision Targa format; tga stands for Targa, which is a video capture board.

.tif TIFF file; stands for Tagged Image File Format. Known as “the variable standard” because there are so many kinds of TIFF subformats.

.wpg WordPerfect graphics format.

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Waveform Audio Formats

Every sound has a waveform that describes its frequency, amplitude, and harmonic content.

Waveform audio digitizers capture sound by sampling this waveform thousands of times per second; the samples are stored in a computer file.

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Waveform Audio Formats

WAV - On multimedia PCs, the most common waveform audio filename extension is .wav, which stands for waveform.

AU and SND - The Sun audio format filename extension is .au, and the NeXT format is .snd. These formats are essentially the same, except that .au files do not have file headers to specify different sampling rates and compression formats.

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Waveform Audio Formats

RA and RAM - 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 RealAudio metafile.

AIF, AIFF, AIFC - AIFF stands for Audio Interchange File Format. Apple invented this file format to create and play audio files on the Macintosh.

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Waveform Audio Formats

MIDI Synthesizer Format (MID) - 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.

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Waveform Audio Formats

MP3 - MP3 is one of the most popular audio formats on the Internet. MP3 stands for MPEG audio layer 3. It’s an audio file format that uses an MPEG audio codec to encode (compress) and decode (decompress) recorded music. MP3 can compress a CD-audio track into a substantially smaller-sized file requiring significantly less bandwidth.

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MIDI Synthesizer Format

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.

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Video Formats

When a movie gets digitized into a computer file, the digital data stream is enormous. To conserve filespace and thereby reduce the bandwidth required to transmit the movie, the video gets compressed.

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Video Formats Video Compression Schemes

YUV subsampling - Divides the screen into little squares and averages color values of the pixels in each square.

Delta frame encoding - Shrinks data by storing only the information that changes between frames; for example, if the background scene does not change, there is no need to store the scene again.

Run length encoding - Detects a “run” of identical pixels and encodes how many occur instead of recording each individual pixel.

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Video Formats

AVI - The most common video format in the Windows world is Microsoft’s AVI, which has the .avi filename extension. AVI stands for audio/video interleave, which describes a clever scheme in which audio frames are interleaved with the video.

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Video Formats

MOV and QT - Because of its cross-platform capabilities, QuickTime has become very popular on the Internet. The filename extensions of QuickTime movies are .qt and .mov.

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Video Formats

MPG, MPEG, and MPE - 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 International Standards Organization committee that created it.

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Video Formats

RM - RealVideo follows the real-time streaming protocol (RTSP) that RealNetworks invented for streaming audio and video over the Internet, the filename extension is .rm.

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Animation Formats

Animation is the use of a computer to create movement on the screen. There are several ways to bring Web pages to life through animation.

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Animation Formats

Animated GIFs - Animated GIFs are a special kind of GIF file (known as GIF89a) that may contain multiple images that get shown in a sequence at specific times and locations on the screen. A looping option causes your Web browser to keep showing the frames in the GIF file continually, and as a result, you see an animation on screen.

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Animation Formats

JavaScript - As noted earlier, Java is a programming environment used to create little applications known as applets that can be downloaded along with a Web page. One of the main uses of applets is to make Web pages become animated.

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Animation Formats

QuickTime - Apple Computer Corporation has created a plug-in whereby QuickTime movies can be embedded as animation objects on Web pages. Both Netscape Communicator and Microsoft Internet Explorer support this plug-in.

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Animation Formats

Shockwave - Macromedia’s Director is the undisputed leader in multimedia animation. Shockwave is a Macromedia product that enables animations created with Director, Authorware, and Flash to plug in to Web pages.

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C H A P T E R 12 Portable

Document Format (PDF)

PDF - 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. PDF files are created by scanning printed documents into bitmaps that work like photographs of the printed pages.

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Avoiding the Pitfall of Renaming Filename Extensions

When you save a file you can change the name of the file. Be careful, however, not to rename the filename extension. Remember that your computer looks

at the filename extension to determine what application will be used to handle the file. Renaming the filename extension will only confuse your computer when you try to access the file.