[derekp7]

And VCRs too. The original Macrovision technique relied on the low tolerance to noise in the old record-mode AGC circuits on first generation VCRs. But when VCRs improved to the point that Macrovision was ineffective, legislation was passed so that VCR manufactures had to include a special circuit to recognize the Macrovision noise bursts, and emulate the old behavior. (Source: my memory of an old article in an electronics magazine, so the above may be somewhat inaccurate -- the article may have been only referring to proposed legislation, or possibly industry self-regulation).

[baddox]

I remember hooking my first DVD player (I had just received for my birthday) to the family TV via an RF modulator, because the DVD player only output RCA and the TV only had a coaxial input. I tried playing The Matrix (the only DVD I had at the time), and the video constantly faded to black and back to normal every few seconds. In retrospect, I gather that was some sort of DRM implemented in the RF modulator, but I don't know if it has anything to do with what you're talking about.