Image Processing Reference
In-Depth Information
Unused bitrate
Apparently a constant bit rate
Program 1
Program 2
Figure 27-3 Statistical multiplexing
shows what happens when you stack the bit-rate graphs for 2 channels. The bit rate for
program 1 has just been plotted from the top axis downward.
There may be times when this technique doesn't deliver the required bit-rate sav-
ings. For example, making sure that the type of material being broadcast on each channel
is very different is a good idea. Grouping 5 music-video channels together or 5 sports
channels that are all likely to be showing content with a lot of motion may detract from
the benefits gained by statistical multiplexing.
From a broadcast engineering point of view, the downside of statistical multiplexing
is that the coding of all 5 streams must take place at the same time in the same system.
Uncompressed content must be delivered, so the feeds to the coder and multiplexer must
have a high bit rate and be of good quality. This increases the amount of wiring that is nec-
Statistical multiplexing is more useful to TV broadcasters than to anyone else. The
source material is likely to be delivered to the coders as SDI video running at 25 Mbps
(also known as DV25). There are higher-bit-rate formats, such as DV50, but these tend to
be used for production processes.
Analog Switch-Off
Digital TV has been broadcast in the United Kingdom for a number of years, and the pene-
tration into households passed 50% in 2004. Analog TV is in declining use and will likely
be discontinued in the foreseeable future. Predictions about when analog TV will be
turned off vary from one country to another, but already citywide TV distribution in
Germany and community-wide broadcasting in Wales have switched to all-digital deliv-
ery. Most other broadcasters are predicting between 10 and 15 years before the demise of
analog TV.
DVD Publishing
DVD is a random-access, file-based storage container. The video is compressed
using MPEG-2 and is then encrypted with the content scrambling system (CSS) algorithm.
Applications that decode this video are widely available for all types of PCs and operating
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