48
49
47
36
TELE-audiovision International — The World‘s Leading Digital TV Industry Publication
— 1 -12/2014
—
MPEG-4 Analysis
47. To analyze the resulting
MPEG-4 signal I hooked up an
Xbox 360 console using the
HDMI connector and started
my favorite game. VLC was
used to get a first idea of the
image quality and to know more
about the used video and audio
CODECs. As can be seen on the
picture, the CW-4412 produces
a perfectly regular H264 –
MPEG-4 AVC (part 10) stream.
48. Trying to understand the
consequences of the bitrate
upon the video quality, I selec-
ted a scene in the game and
toggled the bitrate. Here is the
maximum picture quality, using
a whopping 24000 kbps. Even
with a big zoom on the plant
there are virtually no visible
artefacts.
49. Now the same scene with
the lowest recommended
bitrate for a Full HD stream:
6000 kbps. If you look closely,
you will notice some artefacts,
mainly around edges with high
contrast. But still, the image
quality is fabulous – much
better than MPEG-2 using the
same bitrate.
50. What can be achieved with
variable bitrate (VBR)? These
pictures use an average bit rate
of just 4000 kbps. However, the
video quality is practically as
good as the previous pictures
using a constant bitrate (CBR)
of 6000 kbps. Yet, this means a
25% saving on the bandwidth
and it was no rocket science to
set it up correctly, either. Where
is your excuse to use VBR?
51. Next I wanted to know how
well the CW-4412 manages to
maintain the specified bitrate.
Here we see the CW-4412
working in VBR mode. From the
graph it is easy to spot that the
encoder could easily maintain
the minimum bit rate of just
4000 kbps, having to incre-
ase the bandwidth only when
required.
52. Operating the CW-4412 in
CBR mode at a bit rate of 6000
kbps. The video bitrate is not
100% constant, but the varia-
tion is relatively small.
53. The same at the maximum
bitrate of 24000kbps. No matter
what was happening on the
Xbox 360 game, the graph was
steady.
