Background Image
Previous Page  36 / 164 Next Page
Basic version Information
Show Menu
Previous Page 36 / 164 Next Page
Page Background

48

49

47

36

TELE-audiovision International — The World‘s Leading Digital TV Industry Publication

— 1 -12/2014

TELE-audiovision.com

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.