Multimedia File Formats

Multimedia data and information must be stored in a disk file using formats similar to image file formats. Multimedia formats, however, are much more complex than most other file formats because of the wide variety of data they must store. Such data includes text, image data, audio and video data, computer animations, and other forms of binary data, such as Musical Instrument Digital Interface (MIDI), control information, and graphical fonts. (See the "MIDI Standard" section later in this chapter.) Typical multimedia formats do not define new methods for storing these types of data. Instead, they offer the ability to store data in one or more existing data formats that are already in general use.

For example, a multimedia format may allow text to be stored as PostScript or Rich Text Format (RTF) data rather than in conventional ASCII plain-text format. Still-image bitmap data may be stored as BMP or TIFF files rather than as raw bitmaps. Similarly, audio, video, and animation data can be stored using industry-recognized formats specified as being supported by that multimedia file format.

Multimedia formats are also optimized for the types of data they store and the format of the medium on which they are stored. Multimedia information is commonly stored on CD-ROM. Unlike conventional disk files, CD-ROMs are limited in the amount of information they can store. A multimedia format must therefore make the best use of available data storage techniques to efficiently store data on the CD-ROM medium.

There are many types of CD-ROM devices and standards that may be used by multimedia applications. If you are interested in multimedia, you should become familiar with them.

The original Compact Disc first introduced in early 1980s was used for storing only audio information using the CD-DA (Compact Disc-Digital Audio) standard produced by Phillips and Sony. CD-DA (also called the Red Book) is an optical data storage format that allows the storage of up to 74 minutes of audio (764 megabytes of data) on a conventional CD-ROM.

The CD-DA standard evolved into the CD-XA (Compact Disc-Extended Architecture) standard, or what we call the CD-ROM (Compact Disc-Read Only Memory). CD-XA (also called the Yellow Book) allows the storage of both digital audio and data on a CD-ROM. Audio may be combined with data, such as text, graphics, and video, so that it may all be read at the same time. An ISO 9660 file system may also be encoded on a CD-ROM, allowing its files to be read by a wide variety of different computer system platforms.

The CD-I (Compact Disc-Interactive) standard defines the storage of interactive multimedia data. CD-I (also called the Green Book) describes a computer system with audio and video playback capabilities designed specifically for the consumer market. CD-I units allow the integration of fully interactive multimedia applications into home computer systems.

A still-evolving standard is CD-R (Compact Disc-Recordable or Compact Disc-Write Once), which specifies a CD-ROM that may be written to by a personal desktop computer and read by any CD-ROM player.

For more specific information on multimedia, refer to the articles on the RIFF, DVI, QuickTime, and MPEG multimedia formats.

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