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The World’s Largest Digital TV Trade Magazine
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MPEG-4 Analysis<br />
47<br />
47. To analyze the resulting<br />
MPEG-4 signal I hooked up an<br />
Xbox 360 console using the<br />
HDMI connector and started<br />
my favorite game. VLC was<br />
used to get a first idea of the<br />
image quality and to know more<br />
about the used video and audio<br />
CODECs. As can be seen on the<br />
picture, the CW-4412 produces<br />
a perfectly regular H264 –<br />
MPEG-4 AVC (part 10) stream.<br />
48. Trying to understand the<br />
consequences of the bitrate<br />
upon the video quality, I selected<br />
a scene in the game and<br />
toggled the bitrate. Here is the<br />
maximum picture quality, using<br />
a whopping 24000 kbps. Even<br />
with a big zoom on the plant<br />
there are virtually no visible<br />
artefacts.<br />
49. Now the same scene with<br />
the lowest recommended<br />
bitrate for a Full HD stream:<br />
6000 kbps. If you look closely,<br />
you will notice some artefacts,<br />
mainly around edges with high<br />
contrast. But still, the image<br />
quality is fabulous – much<br />
better than MPEG-2 using the<br />
same bitrate.<br />
50. What can be achieved with<br />
variable bitrate (VBR)? These<br />
pictures use an average bit rate<br />
of just 4000 kbps. However, the<br />
video quality is practically as<br />
good as the previous pictures<br />
using a constant bitrate (CBR)<br />
of 6000 kbps. Yet, this means a<br />
25% saving on the bandwidth<br />
and it was no rocket science to<br />
set it up correctly, either. Where<br />
is your excuse to use VBR?<br />
51. Next I wanted to know how<br />
well the CW-4412 manages to<br />
maintain the specified bitrate.<br />
Here we see the CW-4412<br />
working in VBR mode. From the<br />
graph it is easy to spot that the<br />
encoder could easily maintain<br />
the minimum bit rate of just<br />
4000 kbps, having to increase<br />
the bandwidth only when<br />
required.<br />
52. Operating the CW-4412 in<br />
CBR mode at a bit rate of 6000<br />
kbps. The video bitrate is not<br />
100% constant, but the variation<br />
is relatively small.<br />
53. The same at the maximum<br />
bitrate of 24000kbps. No matter<br />
what was happening on the<br />
Xbox 360 game, the graph was<br />
steady.<br />
48<br />
49<br />
36 <strong>TELE</strong>-<strong>audiovision</strong> International — The World‘s Leading Digital TV Industry Publication — 11-12/2014 — www.<strong>TELE</strong>-<strong>audiovision</strong>.com
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