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Satellite or digital cable
Recording satellite or digital cable signals on a digital video recorder is more
complex than recording analog signals or broadcast digital signals. This is so
because the MPEG-2 or MPEG-4 stream is usually encrypted to prevent people from
viewing the content without paying for it (usually via subscription).
The satellite or cable set-top box does two things. First, it decrypts the
signal. Second, it decodes the MPEG stream into an analog, DVI, or HDMI signal
for viewing on the television. In order to record cable/satellite digital
signals you must get the signal after it is decrypted, but before it is decoded
(between steps one and two); this is how DVRs built into set-top boxes work.
An alternative is that some satellite or (more commonly) cable set-top boxes
have a FireWire port that can be connected to a computer. The recorded MPEG
stream can be relayed to the computer via this FireWire port; though it can be
done live, this is more commonly used for transferring shows from a set-top box
with built-in DVR. (For instructions on doing this on a popular set-top box with
DVR, please see the Wikibook entry How to use a Motorola DVR; some of the ideas
there may apply to other set-top boxes as well.)
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