Digital video compression techniques have played an important role in the world of telecommunication and multimedia systems where bandwidth is still a valuable commodity. Hence, video coding techniques are of prime importance for reducing the amount of information needed for a picture sequence without losing much of its quality, judged by the human viewers. Modern compression techniques involve very complex electronic circuits and the cost of these can only be kept to an acceptable level by high volume production of LSI chips. Standardisation of the video compression techniques is therefore essential.

Straightforward PCM coding of TV signals at 140 Mbit/s was introduced in the 1970s. It conformed with the digital hierarchy used mainly for multichannel telephony but the high bit rate restricted its application to TV programme distribution and studio editing. Digital TV operation for satellites became attractive since the signals were compatible with the time-division multiple access systems then coming into use. Experimental systems in 1980 used bit rates of about 45 Mbit/s for NTSC signals and 60 Mbit/s for the PAL standard.

An analogue videophone system tried out in the 1960s had not proved viable, but by the 1970s it was realised that visual speaker identification could substantially improve a multiparty discussion and videoconference services were considered. This provided the impetus for the development of low bit rate video coding. With the available technology in the 1980s, COST211 video codec, based on differential pulse code modulation (DPCM) was standardised by CCITT, under the H.120 standard. The codec's target...