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What
is Macrovision ?
Macrovision
is a kind of analogue copy-protection system to prevent commercial
DVD/VHS contents being copied to VHS. However, Macrovision
produces distortion patterns when you try to record content
from DVD/VHS systems. It should not prevent normal playback
for most DVD systems. Macrovision, does occasionally, prevent
genuine playback of DVDs on computer systems (eg. when your
TV does not have S-Video or composite inputs, and you must
output through a device, such as your VCR), and this guide
tries to help those who have trouble with this.
Disclaimer
: The aim of this guide is to provide instructions for the
genuine playback of DVDs on computer graphics systems that
either have locked out DVD playback or for people who must
reroute their connections throught their VCR in order to have
basic playback. Any copy-protection method that infringes
on the consumer's right to have proper and genuine use is
deemed to be illegal - hence Macrovision IS illegal if it
prevents proper playback of DVDs. Please do not use this guide
for illegal purposes. This site shall not be responsible for
any legal matters that my arise.
MACROVISION
PROTECTION GUIDE
About
the Author:
Antti
Paarlahti
E-Mail: ap105053@cs.tut.fi
Version:
1.1 Copyright (c) 1992-1995 by Antti Paarlahti This file may
be freely distributed in electronic form as long as it stays
complete.
Introduction
This
FAQ has been built upon my "Macrovision explained" article
that I originally posted to rec.video (22-Oct-1993). That
contained only a raw version of the technical section.
Version
1.0 (3-Dec-1993) of the FAQ introduced a "reader-friendly
front-end", i.e. an explanation for general audiences without
technical background.
Also
some modifications and editions were done to the technical
section. This version, v1.1 (15-dec-1994), has additional
questions and general information, also minor modifications
to the technical section.
Some
material has been acquired from the Net and some (most) from
my own experiments. New contributions AND new questions are
most welcome.
Grammar
corrections are accepted, because I am not a native speaker
of English. Information presented here should be correct as
far as I know, but utter rubbish may have crept in, so proceed
carefully.
How
does it looks like ?
When
dubbing a protected tape, the picture that has gone through
the recording VCR will get dark and then normal again periodically.
The picture may also become unstable when it is at its darkest.
Some televisions do not like Macrovision either; the top of
the picture might be unstable all the time and the colors
may flicker. It resembles very much a mistracked tape. If
you have a TV that has an adjustement for picture height or
vertical hold, you can play with those. Macrovision signals
can be seen as very bright and very dark regions (vertical
stripes) near the top of the picture.
Is
there an easy and economical way to get rid of it?
Not
really.
There
are three main alternatives:
Modify
the VCR. It is easy in principle, just change the value of
one capacitor or resistor in the destination deck. The problem
is, you'd probably have to get a service manual to find out
which one. Furthermore, you still don't get rid of the protection;
it just makes the copying possible.
Make
an eliminator yourself. It is a relatively straightforward
task (more in the technical section), IF you know electronics.
Most people don't, unfortunately.
Buy
a commercial "stabilizer". This method is definitely easy,
but not the cheapest. There have been observations that there
are less and less commercial boxes available. That is because
Macrovision holds patents for the Macrovision process AND
the most obvious ways to defeat it, so they can sue the companies
that manufacture the eliminators. In fact, they have been
doing just that, so many of the companies are now out of business.
Of course you could always buy a time-base corrector or other
legal device that recreates the sync signals. The downside
is that they aren't usually known for their small price....
A
non-technical explanation
Here
is a simple explanation of how the method works. It exploits
the automatic gain control (AGC) circuit in the recorder.
The purpose of the AGC is to adjust the level of the video
signal in such a way that the recording capabilities of the
tape are fully used. This means that weak signals are amplified
and strong ones are attenuated. In the Macrovision method,
some new signals are inserted in the non-visible portion of
the picture. These signals can make the VCR think that a perfectly
normal picture is suddenly way, way too bright. The AGC circuit
therefore darkens it until it thinks the brightness is normal.
Of course, now the REAL picture is very dark. The picture
is varied between bright and dark periodically in order to
defeat simple eliminators that would just amplify the dark
and murky signal back to almost normal. In fact, there was
an early version of the method which had a static level of
brightness, but it was easy to readjust the AGC gain setting
inside the VCR. The level shifting was obviously added fairly
soon after that discovery. Why isn't the TV affected? Well,
most TV sets do not have any AGC-circuits at all, and the
rest behave differently from VHS ones.
My
friend has a VHS VCR that is not affected. How is this possible?
The
proper behaviour of the AGC-circuit is very important in order
to achieve good protection. Apparently the specifications
were somewhat "loose" in the pre-Macrovision days, so the
old (how old?) machines are not affected. JVC, the VHS license
holder, has tightened the spec and the control, so it is difficult
to get an "immune" VCR, but there are some machines that are
conveniently "out of spec". No, I don't know which ones.
I
have heard that 8mm video is not affected by it. Is this true?
8mm
video is not affected by Macrovision, because it is totally
separate from VHS. There is no need to have AGC circuits that
bear any resemblance to JVC ones.
Of
course, 8mm recorders do not remove the protection, so any
subsequent VHS dub will again be unwatchable.
Can
it be defeated by routing the signal throgh a TV with video
inputs/outputs?
No,
it can't. There were some ancient methods that could be eliminated
with some of the above methods, but they are now long dead.
Macrovision is so integrated in the video signal that these
simple tricks will not work
Will
USA mail-ordered boxes work in Europe?
There
are many mail-order companies in the USA selling those boxes.
Can I buy one and use it in Europe? No, not really. You might
get some improvement, but the protection timings are sufficiently
different to keep it from working properly.
Is
unstable picture on rental tapes due to MacroVision?
My TV does not get a stable picture, when I watch rental tapes.
Could this be a fault of the copy protection? Yes, very likely.
Macrovision signals resemble false synchronization pulses,
and some sets mistake them for the real ones. Also colors
may vanish from the top of the picture. This seems to affect
the newer TVs most; the old "steam engines" have the electronic
equivalent of heavy flywheels in their synchronization circuits,
so they don't get distracted so easily.
Can
Macrovision damage my equipment?
Can
I attenuate it? I've heard that the protection consists of
very bright pulses, some 2-3 times the maximum allowable brightness.
Can it damage my equipment? Can attenuation remove the protection?
The brightness is actually only about 15% over the normal
white level, so no harm will be done. Simply attenuating the
signal won't work, it's not the brightness alone that does
the trick.
IF
YOU ARE INTERESTED IN MORE TECHNICAL EXPLANATION - MAIL
ME AND I WILL SEND IT TO YOU IN MS WORD FORMAT
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