Compression

Compression refers to the process of storing information in a manner that uses less space than usual; compressed files provide the same basic amount of data, audio, and/or video information as the original files, but use fewer bits of storage. Current standards of communication, such as the widespread use of 56.6 kbps modems, necessitate the use of compression techniques for experiencing the audio and video content of the Internet.

Two techniques of compression are lossless and lossy. Lossless compression produces files that, upon decompression, are identical to the original file; that is, little to no information is lost during the process. More widely used, however, is lossy compression, which modifies the original file. Lossy compression techniques take advantage of redundancies in the information being stored in order to represent it efficiently. Instead of encoding every piece of information available, as traditional methods of storing audio and video do (e.g., audiotape, videotape), these techniques encode only momentary changes in audio and/or frame-by-frame changes in video in order to produce files that are smaller than the original. This subtle process is done through an initial encoding process that identifies the “static,” or redundant, information, and afterwards encodes only data representing changes occurring over time. As these changes accumulate, they produce, for instance, movement or even a change of scenery on video. Although this process removes information from the original file, the difference between the original and compressed files is typically undetectable by human auditory and visual senses. MP3s and digital video based on MPEG standards, for example, use lossy compression.

When compressed media files are opened, the information is streamed, or transmitted, to a media player. Players, such as the Windows Media player and RealPlayer, are software programs capable of playing compressed audio and video files stored in numerous formats (see below). In order for a media [Page 82]file to play over the Internet, portions of it are loaded into a temporary storage area in the memory (buffer) of the user's computer and, without being permanently saved to the hard drive, the file is then streamed.