 There are also devices called "stabilizers", "video stabilizers" or "enhancers" available that filter out the Macrovision spikes and thereby defeat the system.The principle of their function lies in detecting the vertical synchronization signal, and forcing the lines occurring during the VBI to black level, removing the AGC-confusing pulses.They can be easily built by hobbyists, as nothing more than a cheap microcontroller together with an analog multiplexer and a little other circuitry is needed.