Videotape (analog) copying is prevented with a Macrovision 7.0 or similar circuit in every player. Macrovision may show up as stripes of color, distortion, rolling, black & white picture, and dark/light cycling. Macrovision creates problems for most TV/VCR combos and some high-end equipment such as line doublers and video projectors.
The general term for a system that prevents taping is APS (Analog Protection System), also sometimes called copyguard. Computer video cards with composite or s-video (Y/C) output must also use APS. Macrovision changes the composite video and s-video output in two ways: the Colorstripe technique creates a rapidly modulated colorburst signal, and the AGC technique inserts pulses in the vertical blanking signal. This confuses the synchronization and automatic-recording-level circuitry in 95% of consumer VCRs. Unfortunately, it can degrade the picture, especially with old or nonstandard equipment. Macrovision was not present on analog component video output of early players, but is now required on component output (AGC only, since there is no burst in a component signal).
The discs themselves contain “trigger bits” telling the player whether or not to enable Macrovision AGC, with the optional addition of 2-line or 4-line Colorstripe. The triggers occur about twice a second, which allows fine control over what part of the video is protected. The producer of the disc decides what amount of copy protection to enable and then pays Macrovision royalties accordingly (several cents per disc). Just as with videotapes, some DVDs are Macrovision-protected and some aren’t.
Inexpensive devices can defeat Macrovision, although only a few work against the more recent Colorstripe feature. These devices go under names such as DVD Red, Video Clarifier, Image Stabilizer, Color Corrector, DVD Red, and CopyMaster. Or you can build your own. Some DVD players can be modified to turn off Macrovision output. Professional time-base correctors (TBCs) that regenerate line 21 also remove Macrovision. APS affects only video, not audio.