Page 67 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

44 Chapter 3. Video Coding: Standards

3.3 Chronological Development

Video coding standardization activities started in the early 1980s. The activi-
ties were initiated by the International Telegraph and Telephone Consultative
Committee (CCITT), which is currently known as the International Telecom-
munications Union — Telecommunication Standardization Sector (ITU-T).
This was later followed by CCIR (currently ITU-R), the International
Organization for Standardization (ISO), and the International Electrotechni-
cal Commission (IEC). This has resulted in a number of standards, some of
which are discussed here.

3.3.1 H.120
The /rst video coding international standardization activity was carried out by
Study Group (SG) XV of CCITT during its study period 1980 –1984. In 1984
it issued Recommendation H.120 in its /rst version, and in 1988 it issued the
second version [58]. The standard was targeted for videoconferencing appli-
cations at the digital primary rates of 1:544 Mbits=s and 2:048 Mbits=s. The
standard had three parts: Part 1 for 625=50 regional use at 2 Mbits=s, Part 3
for 525=60 regional use at 1:5 Mbits=s, and Part 2 for international use (both
525=60 and 625=50 at 1:5Mbits=s). Parts 1 and 2 use CR with intra/eld DPCM
for changed regions, whereas Part 3 uses intra/eld prediction, background pre-
1
diction, and motion compensated inter/eld prediction. This di1erence in cod-
ing techniques between the di1erent parts was one of the reasons why H.120
never became a commercial success.

3.3.2 H.261

At the end of 1984, CCITT=SG XV agreed to de/ne a standard targeted
for videophone and videoconferencing applications at ISDN subprimary rates
(≤2 Mbits=s). Initially, it was thought that there would be two di1erent al-
gorithms e,cient at 64 kbits=s or higher and 384 kbits=s or higher, respec-
tively. It was found, however, that a single algorithm could cover all these
rates. Thus, H.261 was drafted in 1989 to provide audiovisual services at
p × 64 kbits=s(p =1 ::: 30). This draft became an international standard in
1991 and was later revised in 1993 [59]. H.261 was the /rst widespread com-
mercial success. In fact, its adopted techniques of hybrid MC-DPCM=DCT
(16 × 16 macroblocks for MC and 8 × 8 blocks for DCT), SKIP=INTER=

1 None of the later standards have included a background prediction mode, although sprite
coding in MPEG-4 can be considered a form of background prediction.