Page 69 - Video Coding for Mobile Communications Efficiency, Complexity, and Resilience

46 Chapter 3. Video Coding: Standards

designed as a toolbox, where the user can decide which tools to use for the
particular application. In addition, the standard de/nes only the decoder and
the bitstream syntax. This allows a large degree of freedom for manufacturers
to propose their own optimized encoders. This generic design and large degree
of freedom have contributed to the success of MPEG-1. It has been used in
a wide range of applications, from interactive systems on CD-ROM to the
delivery of video over telecommunication networks.

3.3.6 MPEG-2

In 1990, ISO=IEC JTC1=SC29=WG11 started studies on a new standard for
applications not covered by MPEG-1. In particular, the new standard was
intended to provide video quality not lower than NTSC=PAL and up to CCIR-
601 quality at rates around 10 Mbits=s. This standardization activity was nick-
named MPEG-2 because it was seen as phase 2 of the work started in
MPEG-1. In 1992, ITU-T=SG 15 joined this standardization e1ort to develop
video coding for Asynchronous Transfer Mode (ATM) networks. In 1993,
it was realized that the scope of MPEG-2 could be enlarged to suit cod-
ing of HDTV. This made an initially planned MPEG-3 for HDTV superJu-
ous. In 1994, the ISO=IEC 13818 (MPEG-2) standard (ITU-T Recommen-
dation H.262) was drafted [63], and later in the year it was accepted as an
international standard. Like MPEG-1, the MPEG-2 standard is generic and
Jexible. In fact, MPEG-2 can be thought of as a superset of, and as such
was designed to be backward compatible with, MPEG-1. There are many
additional features provided by MPEG-2 over MPEG-1, including the sup-
port for interlaced video and scalability. Since implementation of the full
MPEG-2 syntax may not be practical for most applications, MPEG-2 has in-
troduced the concepts of “pro/les,” describing functionalities, and “levels,”
describing resolutions, to provide subset conformance levels. MPEG-2 has
had even more success than MPEG-1, with applications in the areas of ca-
ble TV, networked ATM services, and satellite and terrestrial TV broad-
casting.

3.3.7 H.263
The increasing demand for digital video communications over the public
switched telephone network (PSTN) and mobile networks initiated a new
standardization e1ort by ITU-T=SG 15. The aim was to develop a video cod-
ing standard for low-bit-rate applications below 64 kbits=s. The result of this
e1ort was ITU-T Recommendation H.263 [64], which was completed in 1995
and approved in 1996. Although H.263 was based on the coding structure
of H.261, it provides a signi/cant improvement in performance. Side-by-side