http://en.wikipedia.org/wiki/Macrovision Macrovision's home entertainment technologies are incorporated into the vast majority of all DVD players, digital cable/satellite set-top boxes, personal computers, Digital Video Recorders (DVRs) such as Tivo, and Portable Media Players (PMPs) such as the iPod.
Analog Copy Prevention
A DVD recorder receiving a data stream encoded with Macrovision's legacy ACP copy prevention signal will simply display a message saying the source is "copy-protected", and will pause the recording. This is achieved through a signal implanted within the offscreen range (vertical blanking interval) of the video signal—either physically recorded directly on the tape (as with VHS) or created on playback by a chip in the player (as with DVDs) or the digital cable/satellite box (as with all HDTV programs being down-converted to standard definition). NTSC and other video formats store the video signal as “lines.” A portion of these lines are used for constructing the visible image by transposing them on the screen, but there are approximately 20 to 40 lines outside the visible range that are used for different things in different countries, like closed captioning. Macrovision inserts pulses into this non-displayed area. These signals cause the automatic gain control on the recording VCR to compensate for the varying strength. This makes the recorded picture wildly change brightness, rendering it unwatchable. On most televisions, the viewer on the screen sees no effect in ordinary playback of the modified video because the signal is outside the visible area, but some TVs do not properly blank the vertical retrace and leave dotted white lines near the top of the picture. Some newer TVs also mistake the Macrovision pulses for synchronization pulses. Another modification also used in Macrovision is the addition of colorstripes—rapidly modulated colorburst signals.