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From: dudek@utai.UUCP
Newsgroups: sci.electronics
Subject: Pay TV encoding scheme?
Message-ID: <4030@utai.UUCP>
Date: Mon, 10-Aug-87 19:04:11 EDT
Article-I.D.: utai.4030
Posted: Mon Aug 10 19:04:11 1987
Date-Received: Tue, 11-Aug-87 01:47:53 EDT
Reply-To: dudek@ai.UUCP (Gregory Dudek)
Organization: CSRI, University of Toronto
Lines: 23
Keywords: Pay-TV, encoding, video, code
Summary: How is pay TV encoded


   I've been wondering about this for a while.  How is pay TV
encoded?  It's a screwy scheme since it let's the sound get
through undamaged, but the picture portion of the signal is a mess.
Occassionally the picture looks okay for a few seconds (it seems to
depend on the picture content), then is will get wild (as if the horiz.
hold was twisted with a vengence), sometimes the color (intensities)
are inverted.  I think the encoding must have been chosen to tantalize
non-subscribers since you can hear & see what's happening occasionally.
   I have heard claims that it is done differently in different places,
but from what I can see it looks the same with several companies
in both Toronto & Montreal.
   Do they do this in the US?  Here in Canada cable is *very* common,
additional TV channels (for an extra cost) come encoded this way.  It also
happens to be illegal to build your own decoder, I think.
   My apologies if this has come up before.
   Greg Dudek
-- 
Dept. of Computer Science (vision group)    University of Toronto
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