🚀 go-pugleaf

In article <1992Sep2.133450.18671@panix.com> schuster@panix.com (Michael Schuster) writes:
<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. 
<
<Macrovision inserts very bright pulses in the vertical blank interval.
<Most VCR's use this when setting AGC video level, and get fooled into
<thinking the video levle is much brighter than the picture area really
<is. Most TV's don't. Dunno why.

Why is everyone forgetting the extra horizontal sync pulses BEFORE the
extra white pulses?

If it was only white pulses everything would work just fine.
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