 MPEG-2, MPEG-4, and MPEG-7. relevant and important topic will have an immense affect MPEG-1 and MPEG-2 define methods for the trans- on the future of digital video technologies. mission of digital video information for multimedia and television formats. The MPEG-4 standard, which was 7.4.2 Introduction to video adopted in 1999, specifically addresses the transmission of very low bit rate video by introducing the notion of compression media objects which are made up of audio, visual, or audiovisual content. It is targeted to satisfy the needs of Video or visual communications require significant audiovisual content authors, service providers, and end amounts of information transmission. Video compression users. The MPEG-7 standard, which was adopted in as considered here, involves the bit rate reduction of the 2001, defines audiovisual content storage and retrieval digital video signal carrying visual information. Tradi- services. An aspect central to each of the MPEG stan- tional video based compression like other information dards are the video encoding and decoding algorithms compression techniques, focuses on eliminating re- that make digital video applications practical. dundancy and unimportant elements of the source. The Communications Engineering Desk Reference; ISBN: 9780123746481 Copyright © 2005 Elsevier Inc. All rights reserved CHAPTER 7.4 Video compression degree to which the encoder reduces the bit rate is called Video signals contain information in three dimensions. its coding efficiency, or equivalently its inverse is termed These dimensions are modeled as spatial and temporal the compression ratio, i.e., domains for video encoding purposes. Digital video compression methods generally seek to minimize coding efficiency = (compression ratio) information redundancy independently in each domain. = encoded bit rate/decoded bit rate. The major international video compression standards (MPEG-1, MPEG-2, MPEG-4, H.261, H.262, and (7.4.1) H.263) use this approach. Figure 7.4-1 schematically Compression can