AVS2

FEATURE
New Standard
How to artificially
re-create a HD video
Jacek Pawlowski
HD video
AVS2 is a third generation coding
standard under development
by the Audio Video Coding Standard
Workgroup of China. It will
be a successor of AVS. The AVS
standard is comparable in performance
with the H.264/MPEG-4
AVC commonly used all over the
world for coding HD video. The
tests showed that both standards
achieved almost identical
performance for HD signals. Performance
is here understood as
the PSNR (Peak Signal-to-Noise
Ratio). Only for smaller resolutions
(SD), MPEG-4 proved to be
a little better. An important feature
of the AVS standard is its
lower complexity of the encoder
and decoder what makes it more
practical.
Another reason for China developing
the AVS standard is saving money by
not paying royalties for MPEG-4. Most
of the patents in AVS standard belong
to Chinese companies and organizations.
They charge for them much less
than the Western world companies do
for MPEG-4. In this way, a Chinese
consumer can save maybe 5-10%
when buying a AVS receiver without
MPEG-4 decoder.
But China didn’t stop at AVS and
developed the standard further one.
AVS2 will have a better compression
ratio and thanks to that it will be more
adequate for ultra high definition TV.
Actually, AVS2 can be seen at the Chinese
answer to the new HEVC/H.265
standard published recently by ISO/
IEC and ITU.
In what ways will AVS2 ensure better
performance? Well, the very accurate
explanation is extremely complex, requires
good background in mathematics
and only a narrow group of experts
really can fully understand that. But
what we can understand are at least
the basic concepts underlying the
methods used in AVS2.
Let’s start with the texture analysis
and synthesis. The readers more familiar
with computer games certainly
understand that their software games
synthesize various textures on different
objects required in a game. And
there is no need to store every pixel
of the surface. The software program
can create complex texture knowing
only a small pattern of a bigger area.
New compression algorithms in AVS2
can also do that. And instead of transferring
information of many pixels of
a wavy sea or a distant flowerbed the
AVS2 encoder will analyze what texture
is needed for this part of the picture
and will send to the receiver only
this information (only a small picture).
Now, the decoder in your receiver will
fill in holes in an image by synthesizing
non-repetitive parts of an image, as in
inpainting.
Another interesting method is superresolution
based video coding. To put
it simply, a high resolution image is
reconstructed from multiple sequential
low resolution images. During this
process high frequency modeling as
well as spacial-temporal interpolation
is performed. Interpolation means reconstructing
correct values for an unknown
image pixel located between
known pixels. Located either in space
(left/right/top/bottom) or time (previous/next).
Learning based video coding is maybe
even more interesting. The encoder
analyzes the video sequence in which
one or more objects are moving. It
yields information about size, location
and motion of the objects. Using
computer graphics methods, it creates
models of each object. It sends to the
receiver decoder information about
the model and animation information.
This is sufficient for low resolution video.
To make it suitable for HD video,
some additional information containing
residual pixel signal is sent. This
is simply the difference between the
model and the real image processed
by the encoder.
Except for the above new concepts
described above, there are also more
improvements in the methods and
algorithms used so far. So, AVS2 will
take advantage of: Super-macroblock
prediction, Adaptive Block-size Transform
(ABT), Directional transform, Advanced
motion vector prediction and
Rate Distortion Optimization Quantization
(RDOQ).
We can say that up to the second
generation (AVS and MPEG-4) video
coding standards relied mainly on taking
advantage of various imperfection
of the human eye to achieve high
compression ratio. AVS2 takes a step
further. Some elements of the video
will be in fact computer animations or
computer generated textures resembling
real things. This is another step
away from transmitting the original
video: what you see on your monitor is
a brand new artificially created video,
which looks as the original, but in reality
it is re-created by using only some
parts of the original video.
Compressed video already went
away from a 1:1 transmission, as in
the old analog times (the original is
identical to the copy). Now even less of
the original is needed, to re-created it.
Will AVS2 achieve similar compression
ratio improvement over AVS as
HVEC has demonstrated over MPEG-
4? Can it save up to 50% of the bandwidth?
Some scientific papers report
up to 37% of bandwidth reduction.
This can change because the standard
is not finalized yet and very few test
results have been published. So let’s
see where all this will eventually end.
96 TELE-audiovision International — The World‘s Leading Digital TV Industry Publication — 11-12/2014 — www.TELE-audiovision.com