MPEG-1 to MPEG-4 compression

Digital technologies entered the field of consumer products through audio. The CD disc demonstrated the essential advantages of digital technology: perfect quality, flexibility of information processing, robustness of content. The digital transmission or storage mode required more time-consuming research to solve the problems inherent in the television signal. Digitizing a television signal produces a digital data rate of 160 Mbps. It cannot therefore be transmitted over a conventional channel (satellite, cable or terrestrial) without prior compression. A similar capacity problem arises for storage equipment. Research was therefore carried out in institutional and industrial laboratories to develop high-performance compression algorithms specific to television signals. The results have in fact exceeded expectations. The compression rates achieved are such that, using appropriate modulation techniques, it is possible to transmit several digital TV signals in an analog TV channel (between 6 and 10 signals, depending on the quality required). TV broadcasters can therefore look forward to a drastic reduction in transmission costs, and thus a multiplication of TV channels. This argument is essential to the success of digital multimedia. Other aspects were also important: the possibility of adding additional data, flexibility, encryption with flexible subscriber control (pay-per-view).

Standardization is essential to the success of digital technologies. Indeed, the widespread use of this transmission mode requires equipment interoperability and therefore signal standardization, as in the case of PAL, Secam and NTSC signals. The MPEG (Moving Picture Experts Group) standardization committee therefore brought together experts from academic and industrial laboratories around the world to establish standards adapted to digital audiovisual applications. At the heart of MPEG's work are algorithmic developments aimed at achieving the best compression rates, to ensure optimum use of storage capacity or bandwidth. But MPEG also strives to segment and characterize each type of application, to define the tools needed to realize the functionalities they require.

The process for reaching agreement on the standard follows the following stages: call for proposals from experts to meet the technical requirements of the standard, evaluation of the various proposals, establishment of an initial test model bringing together the best elements of the various proposals, optimization of a common reference model, and finally final agreement on the standard. An MPEG standard specifies two essential points: the stream structure and the decoding method for restoring the audiovisual signal. The selection of the coding modes used is left to the user, who can therefore make his or her own compromise...