Macrovision and RipGuard
Macrovision is a company that creates electronic copy prevention schemes.
Macrovision is notable for its video copy prevention scheme
of the same name. A VHS videotape or
DVD (no laserdisc or video CD players implement it) encoded with Macrovision
will cause a VCR set to
record it to fail. This is usually visible as a scrambled
picture as if the tracking was incorrect or the picture will
fade between overly light and dark.
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).
NTSC and other video
formats store the video signal basically 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 and
SAP alternate
audio.
Macrovision inserts pulses into this non-displayed area.
These signals cause the automatic tracking and 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 use of
the protected 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.
Macrovision is a nuisance to some because it can interfere
with other electronic equipment. If one were to run their
video signal through a VCR before the television, some VCRs
will output a ruined signal regardless of whether or not
it is recording. This also occurs in some TV-VCR combo sets.
The signal also confuses home theater line
doublers (devices for improving the quality of video
for large projection TVs) and some high-end television comb
filters.
Legal Issues
Some DVD players give the user the option of disabling the
Macrovision technology. This is possible since the signal
is not stored on the DVD itself; instead commercial DVDs
just contain an instruction to the player to create such
a signal during playback. Some DVD players can be so configured
as to pay no heed to such instructions.
There are also cheap devices called stabilizers for sale
that filter out the Macrovision spikes and thereby defeat
the system. These products tend not to last long as the Macrovision
company owns patents on both the Macrovision system and the
most common ways of defeating the system, and the company
can and does sue manufacturers of these devices.
The MPAA maintains it has every right to limit copying of
movies, comparing DVDs to pay-per-view where the consumer
is allowed to view the movie in question but nothing more.
Many are concerned that the organization is attempting to
quash fair use by disallowing consumers to make personal
copies.
United States fair use law as interpreted in the decision
over Betamax (Sony Corp. v. Universal City Studios) dictates
that one is fully within their legal rights to copy videos
they own, however the legality has changed somewhat with
the Digital Millennium Copyright Act. In the US starting
on April 26, 2002, no VCR may be manufactured or imported
which does not contain the Automatic Gain Control circuitry
(which makes VCRs vulnerable to Macrovision); this is contained
in title 17, section 1201(k) of the Digital Millennium Copyright
Act. There are a number of older VCR models that are not
affected by Macrovision.
Furthermore, starting on October 26, 2001, the sale, purchase,
or manufacture of any device that disables Macrovision copy
prevention will be illegal under section 1201(a) of the same
act. However, the constitutionality of many of the Act's
provisions is under debate.
RipGuard
In February 2005, Macrovision introduced their new RipGuard
technology. This is designed to prevent (or reduce) digital
DVD copying by altering the format of the DVD content in
such a way as to disrupt the ripping software. Macrovision
claim (http://www.macrovision.com/products/ripguard/index.shtml)
97% of all current DVD rippers will not be able to copy
a DVD protected by RipGuard technology.
Macrovision
Discs can specify that the player use Macrovision, an analog anti-copying mechanism. The
video itself is not Macrovision signaled (unlike Macrovision-enabled
VHS tapes); instead, discs may have an instruction that tells
the DVD player to add the Macrovision signal during playback.
Some DVD players can be configured to disable Macrovision.
Macrovision prevents the consumer from copying the video
onto a VCR tape by using a deliberately-defective signal which
may also cause problems for some projection TV's as well
as older television models. This alone would not prevent
the duplication of DVDs in their entirety without decrypting
the data, given suitable equipment, although "consumer-grade" DVD
writers deny this ability by refusing to duplicate the tracks
on the disc which contain the decryption keys.
From Wikipedia, the free encyclopedia.