2 Information Processing

2.4 The Representation and Processing of Information

Sound Files

Some common types of sound files: .au .aif .mid (midi) .wav .mp3 (Mpeg)

.au (AUdio file) A digital audio file format

from Sun that is used on the Internet and can be played by a Java program.

It provides toll-quality sound and uses the .AU extension.

It generally uses the u-Law (mu-Law) encoding method, and raw u-Law files and AU files are the same except for the file header.

* www.techweb.com

.aiff (Audio Interchange File Format) A digital

audio file format from Apple that is used on the Macintosh.

It uses the .AIF extension and breaks apart the file into chunks.

The Common chunk holds file parameters such as sampling rate, and the Sound Data chunk contains the digital sound.

AIFC and AIFF-C are compressed versions of the format.

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.mid (Musical Instrument Digital Interface) A

standard protocol for the interchange of musical information between musical instruments, synthesizers and computers

It defines the codes for a musical event, which includes the start of a note, its pitch, length, volume and musical attributes, such as vibrato.

MIDI is NOT considered as digital audio. MIDI is not actual sound. It also defines codes for various button, dial

and pedal adjustments used on synthesizers.

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.mid MIDI makes an ideal system for

storing music on digital media due to its small storage requirement compared with digitizing actual music.

Since the advent of General MIDI, a standard for defining MIDI instruments, MIDI has become widely used for musical backgrounds in multimedia applications

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.wav (WAVe file) The native digital audio format

in Windows. Using the .WAV file extension, 8-bit or 16-bit

samples can be taken at rates of 11,025 Hz, 22,050 Hz and 44,100 Hz. The highest quality (16-bit at 44,100 Hz) uses 88KB of storage per second.

Windows uses WAV files for general system sounds, and new WAV files can be placed in the Windows Media folder (\windows\media or \winnt\media) and assigned in the Sounds control panel.

* www.techweb.com

.mp3 (MPEG Audio Layer 3) An audio

compression technology that is part of the MPEG-1 and MPEG-2 specifications. Developed in Germany in 1991 by the Fraunhofer Institute.

MP3 uses perceptual audio coding to compress CD-quality sound by a factor of 12, while providing almost the same fidelity.

MP3 music files are played via software or a physical player that cables to the PC for transfer.

* www.techweb.com

.mp3 MP3 has made it feasible to download

quality audio from the Web very quickly, causing it to become a worldwide auditioning system for new musicians and labels

* www.techweb.com

.mp3 Copyrighted music is also offered for a

fee, or sometimes for free, creating a major legal issue.

MP3 has revolutionized music distribution, since an hour of near CD-quality audio can be downloaded in five minutes.

Major publishers are trying to cope with this phenomenon by introducing copyright protection

* www.techweb.com

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Video Files

Some common types of sound files: .avi .mov .mpg (Mpeg)

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.avi (Audio Video Interleaved) A Windows

multimedia video format from Microsoft.

It interleaves standard waveform audio and digital video frames (bitmaps) to provide reduced animation at 15 fps at 160x120x8 resolution. Audio is 11,025Hz, 8-bit samples.

* www.techweb.com

.mov (QuickTime) Multimedia extensions to the Macintosh

starting with System 7 that add sound and video capabilities.

A QuickTime file can contain up to 32 tracks of audio, video, MIDI or other time-based control information.

Most major Macintosh DBMSs (database management systems) support QuickTime. Apple also provides a version of QuickTime for Windows PCs.

* www.techweb.com

.mpg (MPEG) (Moving Pictures Experts Group)

Pronounced "em-peg." An ISO/ITU standard for compressing video.

MPEG is a lossy compression method, which means that some of the original image is lost during the compression stage, which cannot be recreated.

* www.techweb.com

MPEG-1 MPEG-1, which is used in CD-ROMs

and Video CDs, provides a resolution of 352x288 at 30 fps with 24-bit color and CD-quality sound.

Most MPEG boards also provide hardware scaling that boosts the image to full screen. MPEG-1 requires 1.5 Mbps bandwidth.

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MPEG-2 MPEG-2 supports a wide variety of

audio/video formats, including legacy TV, HDTV and five channel surround sound.

It provides the broadcast-quality image of 720x480 resolution that is used in DVD movies.

MPEG-2 requires from 4 to 15 Mbps bandwidth.

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MPEG-4 MPEG-4 is the next-generation MPEG that goes

far beyond compression methods. Instead of treating the data as continuous

streams, MPEG-4 deals with audio/video objects (AVOs) that can be manipulated independently, allowing for interaction with the coded data and providing considerably more flexibility in editing.

MPEG-4 supports a wide range of audio and video modes and transmission speeds. It also deals with intellectual property (IP) and protection issues.

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AnimationMoving diagrams or cartoons that are

made up of a sequence of images displayed one after the other. Animation files take up much less disk space than a true video sequence.

Frame-based animation Object-based animation

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Frame-based animation a frame is a single image in a sequence of

images The animation is made up of a sequence of

frames rendered continuously at a certain display rate (e.g. a movie is usually rendered at 24 frames per second - fps)

Frame-based animation is used for frames with irregular patterns and realistic pictures.

Frame based animation works similarly to old-fashioned flipbooks. A flipbook contains images, such as a person running that gradually changes over a series of pages.

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Object-based animation If an animation is presenting the motions of

some regular patterns, object-based animation can be used.

Object animation usually involves moving an unchanging object along a path

For example, if the background is keeping unchanged for a number of successive frames, the background can be presented as an object and there is only 1 object frame required for the background in several or all frames.

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Frame-based animation

Object-based animation

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Only 1 plane is required

Frame-based Vs. Object-based

Frame-based Better for realistic

pictures Used for irregular

patterns File size depends

on the resolution and number of frames

Object-based No need to draw

pictures frame by frame

Used for regular/unchanged pattern/object

File size depends on the number of objects and number of frames

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