TELE-audiovision - The World’s Leading Digital TV Industry Publication - page 30

TELE-audiovision International — The World‘s Leading Digital TV Industry Publication
— 1 -12/2014
compressing a video and audio signal
and then converting it into a transport
stream that is finally provided through
the encoder’s ASI output or via IPTV
takes a little time. For pre-recorded
transmissions that can be prepared in
MPEG-4 beforehand this is not much
of an issue, but what about time-crit-
ical transmissions such as the current
time that is shown before the evening
news begins, or live broadcasts? Here,
a delay of a few seconds makes a lot
of difference. Just think of it: Both you
and your neighbour are watching a soc-
cer match. Your neighbour is still on
analog cable and whenever the team
he supports scores a goal you hear him
scream out while your DVB-C receiver
still only shows the ball being passed
from centre forward to forward. Takes
a lot of fun out of the match, doesn’t it?
We created the following test environ-
ment to measure the latency caused by
the CW-4412: A test PC with two video
outputs plays back a test pattern with
an exact timer (30 frames per second).
One output is connected to a standard
monitor, while the second output is led
to one of the two HDMI inputs of the CW-
4412. We chose 1280 x 720 pixels as test
resolution to tread on a middle course
between 1080p and SD, which seemed
reasonable and economical to us.
Next, we connected one of our ref-
erence signal meters to the CW-4412’s
ASI output, while a second reference
meter with integrated IPTV analyser
was used to also receive and look at the
IPTV transport stream simultaneously.
The result was genuinely breathtak-
ing: The CW-4412 provided the com-
pressed MPEG-4 transport stream
through its ASI output less than one
second after the source signal had been
fed to the encoder. What a treat! What’s
more, the measured delay already in-
cludes the time required by the meter
to demodulate and process the trans-
port stream, which adds even more
shine to the CW-4412’s performance.
As far as IPTV is concerned, we
measured a delay of approximately four
seconds. Keep in mind, though, that
this is by no means the encoder’s fault
but lies in the nature of using a physi-
38. CableWorld offers a free Transport
Stream Analyzer software! Yes, you did
read it correctly: the software is free and
does not require any CableWorld specific
hardware. Visit the CableWorld website
right now!
39. As usual with CableWorld software the
application is very structured and orga-
nized in several tabs. The first tab allows
to select the IP address of the multicast
40. The Data Analyzer tab. If you can read
and understand the contents of plain
packets, this is for you.
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