🚀 go-pugleaf

In article <1992Sep2.041037.347@u.washington.edu> bunky@milton.u.washington.edu (Mike) writes:
<
<     
<     Does anyone know how macrovision allows a video tape to be watched on
<     a television but not on a vcr?  I recently looked at a copy protected
<     videotape and it appeared that there were 4 white bars on the last
<     8 or 9 lines in the vertical interval that periodicly (every 15 or 20
<     sec) faded in and out.  It looks like it's changing the average level
<     of the picture to mess up the vcr.  If that's the case could this be
<     fixed with a clamping circuit or some kind of dc restorer circuit?
<     If anyone knows the technical details of how the copy protection scheme
<     works I would be very interested. 

I posted how Macrovision works a little bit ago.

What you can't see are the extra horizontal sync pulses right before the white
pulses.  Those and the white pules are what affect the VCR that tries to dub
the protected tape.
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