131 Why bother having an MPEG-2 ?
Description
This article is from the MPEG FAQ, by Frank Gadegast phade@cs.tu-berlin.de with numerous contributions by others.
131 Why bother having an MPEG-2 ?
MPEG-1 was optimized for CD-ROM or applications at about 1.5
Mbit/sec. Video was strictly non- interlaced (i.e. progressive). The
international cooperation executed well enough for MPEG-1, that the
committee began to address applications at broadcast TV sample rates
using the CCIR 601 recommendation (720 samples/line by 480 lines per
frame by 30 frames per second or about 15.2 million samples/sec
including chroma) as the reference.
Unfortunately, today's TV scanning pattern is interlaced. This
introduces a duality in block coding: do local redundancy areas
(blocks) exist exclusively in a field or a frame.(or a particle or
wave) ? The answer of course is that some blocks are one or the other
at different times, depending on motion activity. The additional man
years of experimentation and implementation between MPEG-1 and MPEG-2
improved the method of block-based transform coding.
It is often remarked that MPEG-2 spent several hundred man years and
10s of millions of dollars yet only gained 20% coding efficiency over
MPEG-1 for interlaced video signals. However, the collaborative
process brought companies together, and from that came a standard well
agreed upon. In many ways, the political achievement dwarfs the
technical one. Also, MPEG-2 was exploratory. Coding of interlaced
video was unknown territory. It took some considerable convincing to
demonstrate that a simple syntax, akin to MPEG-1, was as efficient as
other proposals. Left by themselves, each company would probably have
produced a diverse scope of syntax.
Continue to:
My Books
