19
20
21
22
24
TELE-audiovision International — The World‘s Leading Digital TV Industry Publication
— 1 -12/2014
—
light, there’s also shadow,
and in the case of CBR easy
calculation comes at the
expense of changing video
quality. The bit rate require-
ments of fast camera move-
ments or dynamic video con-
tent may easily exceed the
pre-set constant bitrate (un-
less it equals the maximum
bit rate, which generally
is not the case and would
waste valuable resources
whenever more static con-
tent is transmitted), causing
the dreaded block artefacts
none of us likes to see.
This is where VBR kicks
in: Whenever video content
does not change much, the
required bit rate decreases
because only few image de-
tails need to be compressed.
And when all of a sudden dy-
namic changes in the video
content occur the bit rate in-
creases alongside so that the
intended video quality after
compression can be main-
tained. On average, the bit
rate with VBR is lower than
with CBR.
And there’s another ben-
efit with VBR: The chance
that several variable bit
rates within a single trans-
port stream all peak at the
very same time is rather low,
which means that the overall
bandwidth of a transpond-
er’s transport stream with
VBR signals can be smaller,
while the video quality of the
individual signals is higher.
Sounds perfect, right? Yes,
in theory. In the real world,
however, VBR comes with
some strings attached. For
example, the encoder has
to know the low and high
bit rate limits that must not
be exceeded. Those limits,
however, depend entirely
on the average bit rate. This
means the encoder must an-
alyse the video signal based
Web Frontend
19. ENCODER – VIDEO & AUDIO SETUP: This menu option allows
to independently configure the output signal. You can select bet-
ween a constant bitrate (CBR) or a variable bitrate (VBR). Also, you
can change other relevant MPEG-4 parameters.
20. ENCODER – MULTIPLEX SETUP: Here you can select the
required PIDs for the output stream. This comes very handy, as
you can avoid problems with multiplexers, if you configure the
PIDs correctly at this stage. Being able to input the desired service
name and service provider name is just perfect.
21. IP STREAMER – IP STREAMER SETUP: Next you can configure
the IP streaming, again independently for each encoder. Just select
the mode (Multicast or Unicast) and specify the relevant IP and port
and you are set.
22. SETTINGS – WEB INTERFACE SETTINGS: This option lets you
configure the network settings for the web interface. The CW-4412
can be controlled through a browser or by means of free applica-
tions provided by CableWorld. Both use independent networking
configurations, which is actually very convenient. If you cannot
access one network, for whatever reason, you can still communi-
cate with the CW-4412 through the alternative way.
