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DVD Copy Protection

N

Norm Dresner

Jan 1, 1970
0
In addition to being an engineer, I'm also a consumer and I've run into a
situation that I'm curious about. A friend gave us a new DVD player as a
Christmas present which had only audio/video outputs. Since our TV set is
an older model (circa 1986) , it lacks these inputs but our VCR had them so
I glibly plugged the DVD player into it and tried to watch a DVD. Of
course, it doesn't work and the DVD player manual explicitly says that it
won't because of copy-protection.

I'm not looking to break the system -- I fully intend to buy a new TV set --
but I'm technically curious. What are they doing to the signal that makes
it acceptable to a TV set but unusable to a VCR? I'd assume they're mucking
with the sync signals but how does one work and not the other?

TIA
Norm
 
J

Jim Thompson

Jan 1, 1970
0
In addition to being an engineer, I'm also a consumer and I've run into a
situation that I'm curious about. A friend gave us a new DVD player as a
Christmas present which had only audio/video outputs. Since our TV set is
an older model (circa 1986) , it lacks these inputs but our VCR had them so
I glibly plugged the DVD player into it and tried to watch a DVD. Of
course, it doesn't work and the DVD player manual explicitly says that it
won't because of copy-protection.

I'm not looking to break the system -- I fully intend to buy a new TV set --
but I'm technically curious. What are they doing to the signal that makes
it acceptable to a TV set but unusable to a VCR? I'd assume they're mucking
with the sync signals but how does one work and not the other?

TIA
Norm

What does "doesn't work" mean? Picture changing brightness and
flopping in and out of sync? If that's the case, it's Macrovision.
Just buy a Macrovision killer... they're cheap.

...Jim Thompson
 
C

Costas Vlachos

Jan 1, 1970
0
Norm Dresner said:
In addition to being an engineer, I'm also a consumer and I've run into a
situation that I'm curious about. A friend gave us a new DVD player as a
Christmas present which had only audio/video outputs. Since our TV set is
an older model (circa 1986) , it lacks these inputs but our VCR had them so
I glibly plugged the DVD player into it and tried to watch a DVD. Of
course, it doesn't work and the DVD player manual explicitly says that it
won't because of copy-protection.

I'm not looking to break the system -- I fully intend to buy a new TV set --
but I'm technically curious. What are they doing to the signal that makes
it acceptable to a TV set but unusable to a VCR? I'd assume they're mucking
with the sync signals but how does one work and not the other?

TIA
Norm


Same thing happens in satellite digital TV here in the UK, where certain
"pay-per-view" movies are copy-protected and supposedly cannot be recorded
on VCRs. I've tried recording these on my VCR and they recorded fine... It
could be that modern VCR manufacturers have agreements with the movie
companies and cable/satellite networks and have special circuitry that
recognises certain signals hidden in the video signal and scrambles it. This
is pure guessing though, I don't know how it's done. But as said above, I am
able to successfully record the copy-protected satellite TV movies, so it
seems to be something that depends on the type/brand of VCR.

cheers,
Costas
 
R

Ron G

Jan 1, 1970
0
Hi Jim---

Where are they available at?

Special Internet stores, or local electronics stores?

Are there various updates?
I had never heard of them, before reading your post.

Thanks and Best to you---
Ron
 
J

Jim Thompson

Jan 1, 1970
0
Hi Jim---

Where are they available at?

Special Internet stores, or local electronics stores?

Are there various updates?
I had never heard of them, before reading your post.

Thanks and Best to you---
Ron
[snip]

Surf for "Sync Stabilizers". They're pretty easy to make, if you're
fairly conversant in video formats. It's as simple as cleaning up
garbage added in the VBI (vertical blanking interval).

A few starting places...

http://www.repairfaq.org/filipg/LINK/F_MacroVision.html
http://www.kolumbus.fi/pami1/macrovision/
http://www.facetvideo.com/
http://www.dvdrhelp.com/dvdhacks.php
http://www.satalogue.com/section6/page0.htm
http://www.digital-digest.com/dvd/articles/macrovision_general.html
http://www.220giftcenter.com/dvd5800.htm

...Jim Thompson
 
J

Joel Kolstad

Jan 1, 1970
0
Norm Dresner said:
I'm not looking to break the system -- I fully intend to buy a new TV set
-- but I'm technically curious. What are they doing to the signal that
makes it acceptable to a TV set but unusable to a VCR? I'd assume
they're mucking with the sync signals but how does one work and not the
other?

(Assuming it's Macrovision, as already described by Jim Thompson...)

The automatic gain control on the video signal inputs on VCRs has a much
slower response than that of a TV. This is due to the fact that VCRs have
to deal with physical media -- tape -- that tends to suffer sometimes rapid
signal level variations due to mechanical misalignment, aging tape, etc. so
the slow AGC time-constant 'evens out' these variations.

Macrovision, at its simplest level, places very high average level signals
into the video lines during the vertical blanking interval of the frame,
then slowly moves to placing very low average level signals there, and
repeating. This causes the a VCR to first noticeably crank down its AGC,
then crank it up again, etc. -- but with a time-constant on the order of
several frames. Hence you see alternating dark and bright images on your
TV.

When a macrovision tape is directly connected to a TV, the TV's faster AGC
recovers quickly enough so that -- within a few _lines_ of being outside of
the vertical blanking interval -- the AGC level is 'correct' and you view
the picture as intended.

It's not a perfect system. There used to be lists of VCRs that had faster
AGCs that weren't particularly affected by Macrovision (as well as a few
professional units that had manually set gain controls), but at some point
various operating parameters of VCRs were 'harmonized' and most all units
today are affected. Likewise, there were some TVs that had comparatively
slow AGCs and wouldn't work with Macorvision either, but this too is now
more of a historical curiosity.

The cheap 'Macrovision killer' boxes out there just wait for the vertical
blanking interval and then clamp the video level of each line to a fixed
value, thereby not causing the AGC in the VCR to get thrown out of whack.

There's tons of information about this on the Internet, and Macrovision
themselves has a web site too. New versions of Macrovision are presumably
more robust than the original (there have been many different versions over
time), but there's still only so much they can do while keeping the signal
compatible with a regular TV set. What I find amazing is that the
Macrovision guys talked the DVD player guys into _adding_
Macrovision-encoded outputs to the players -- hence everyone who purchases a
DVD player is paying to have some of their rights to produce back-up copies
of a DVD taken away. (Even though I would be the first to admit that about
99% of people attempting to defeat Macrovision or any other copy protection
scheme do so strictly with the intent to pirate the content.)

---Joel Kolstad
 
J

John Tserkezis

Jan 1, 1970
0
Norm said:
In addition to being an engineer, I'm also a consumer and I've run into a
situation that I'm curious about. A friend gave us a new DVD player as a
Christmas present which had only audio/video outputs. Since our TV set is
an older model (circa 1986) , it lacks these inputs but our VCR had them so
I glibly plugged the DVD player into it and tried to watch a DVD. Of
course, it doesn't work and the DVD player manual explicitly says that it
won't because of copy-protection.

I'm not looking to break the system -- I fully intend to buy a new TV set --
but I'm technically curious. What are they doing to the signal that makes
it acceptable to a TV set but unusable to a VCR? I'd assume they're mucking
with the sync signals but how does one work and not the other?

As well as Macrovision copy protection as others have mentioned in this
thread, there is CGMS. (Copy Protection Management System) It's encoded
within the sync frame, and is only really useful against systems that
specifically look for it. (Doesn't stop tape duplication)
My PVR detects it, and as such, a "normal" DVD player won't work regardless
of macrovision status.
 
I

Iwo Mergler

Jan 1, 1970
0
Joel said:
(Assuming it's Macrovision, as already described by Jim Thompson...)

The automatic gain control on the video signal inputs on VCRs has a much
slower response than that of a TV. This is due to the fact that VCRs have
to deal with physical media -- tape -- that tends to suffer sometimes rapid
signal level variations due to mechanical misalignment, aging tape, etc. so
the slow AGC time-constant 'evens out' these variations.

Macrovision, at its simplest level, places very high average level signals
into the video lines during the vertical blanking interval of the frame,
then slowly moves to placing very low average level signals there, and
repeating. This causes the a VCR to first noticeably crank down its AGC,
then crank it up again, etc. -- but with a time-constant on the order of
several frames. Hence you see alternating dark and bright images on your
TV.

When a macrovision tape is directly connected to a TV, the TV's faster AGC
recovers quickly enough so that -- within a few _lines_ of being outside of
the vertical blanking interval -- the AGC level is 'correct' and you view
the picture as intended.

It's not a perfect system. There used to be lists of VCRs that had faster
AGCs that weren't particularly affected by Macrovision (as well as a few
professional units that had manually set gain controls), but at some point
various operating parameters of VCRs were 'harmonized' and most all units
today are affected. Likewise, there were some TVs that had comparatively
slow AGCs and wouldn't work with Macorvision either, but this too is now
more of a historical curiosity.

Most modern recording devices don't have the AGC problems
any more. In fact, the Macrovision signal is recognised
by a specialised circuit and it's effect on old AGC circuitry
is emulated to stop copying. These days, you can regard
Macrovision as a do-not-copy flag.

Kind regards,

Iwo
 
J

Jan Panteltje

Jan 1, 1970
0
(Assuming it's Macrovision, as already described by Jim Thompson...)

The automatic gain control on the video signal inputs on VCRs has a much
slower response than that of a TV. This is due to the fact that VCRs have
to deal with physical media -- tape -- that tends to suffer sometimes rapid
signal level variations due to mechanical misalignment, aging tape, etc. so
the slow AGC time-constant 'evens out' these variations.
That is actually not correct.
The modulation is FM, so the output signal is not depending
on the signal strength from the tape.
(but chroma is converted down and superimposed on the FM carrier).
The AGC is in the INPUT chain.
The AGC is only there to adjust the (can be any value almost) input
video level so the FM carrier deviation is norm when recording.
I published a macro vision remover with a PIC and 74HC4053 some month ago
on alt.satellite.tv.crypt. (for the vertical interval pulses type).
A build one is available from me for 40 Euro.

The cheap 'Macrovision killer' boxes out there just wait for the vertical
blanking interval and then clamp the video level of each line to a fixed
value, thereby not causing the AGC in the VCR to get thrown out of whack. correct

What I find amazing is that the
Macrovision guys talked the DVD player guys into _adding_
Macrovision-encoded outputs to the players -- hence everyone who purchases a
DVD player is paying to have some of their rights to produce back-up copies
of a DVD taken away.
Making a digital backup is no problem, most stuff is digital these days, DVD players
are much cheaper then VHS now.
 
P

Paul Hovnanian P.E.

Jan 1, 1970
0
Norm said:
In addition to being an engineer, I'm also a consumer and I've run into a
situation that I'm curious about. A friend gave us a new DVD player as a
Christmas present which had only audio/video outputs. Since our TV set is
an older model (circa 1986) , it lacks these inputs but our VCR had them so
I glibly plugged the DVD player into it and tried to watch a DVD. Of
course, it doesn't work and the DVD player manual explicitly says that it
won't because of copy-protection.

I'm not looking to break the system -- I fully intend to buy a new TV set --
but I'm technically curious. What are they doing to the signal that makes
it acceptable to a TV set but unusable to a VCR? I'd assume they're mucking
with the sync signals but how does one work and not the other?

Hmm. Strange. My VCR will pass a Macrovision protected video signal from
video in to video out or the modulator. It just won't record properly.
I'm assuming that this is what you are trying to do (with the VCR's RF
modulator).
 
J

Joel Kolstad

Jan 1, 1970
0
Luhan Monat said:
Today's DVD players generate Macrovision II. There are two components.

2) 4 out of every 20 or so lines has their Chroma Burst signal phase
inverted.

And do you happen to know why _this_ doesn't seriosuly mess up the PLL in
the TV and thereby distort the colors?

---Joel Kolstad
 
L

Luhan Monat

Jan 1, 1970
0
Norm said:
In addition to being an engineer, I'm also a consumer and I've run into a
situation that I'm curious about. A friend gave us a new DVD player as a
Christmas present which had only audio/video outputs. Since our TV set is
an older model (circa 1986) , it lacks these inputs but our VCR had them so
I glibly plugged the DVD player into it and tried to watch a DVD. Of
course, it doesn't work and the DVD player manual explicitly says that it
won't because of copy-protection.

I'm not looking to break the system -- I fully intend to buy a new TV set --
but I'm technically curious. What are they doing to the signal that makes
it acceptable to a TV set but unusable to a VCR? I'd assume they're mucking
with the sync signals but how does one work and not the other?

TIA
Norm
Today's DVD players generate Macrovision II. There are two components.

1) large data pulses a placed in the Video Blanking Interval and effect
the AGC in most VCRs.

2) 4 out of every 20 or so lines has their Chroma Burst signal phase
inverted.

Clamping down the data pulses in (1) along with simply removing the
errant color burst on the offencing lines renders the signal clean
enough for good recording.

But hey, this is all just theoretical unless someone was really good
with a PIC16F628.
 
R

Roy Battell

Jan 1, 1970
0
Joel Kolstad said:
And do you happen to know why _this_ doesn't seriosuly mess up the PLL in
the TV and thereby distort the colors?

Damn-it - on My 4 year old Toshiba it does, with direct SCART
connection from a Pioneer DVD player with NTSC movies even
using RGB.
Forcing the player to output PAL solved the problem
As it says in the logo 'Macrovision - quality protection' -
i.e. you don't get any :-(
 
F

FrAgFo0d

Jan 1, 1970
0
Damn-it - on My 4 year old Toshiba it does, with direct SCART
connection from a Pioneer DVD player with NTSC movies even
using RGB.
Forcing the player to output PAL solved the problem
As it says in the logo 'Macrovision - quality protection' -
i.e. you don't get any :-(

--

How about LG?
 
J

Joel Kolstad

Jan 1, 1970
0
Jan Panteltje said:
That is actually not correct.
The modulation is FM, so the output signal is not depending
on the signal strength from the tape.

Yes, it occurred to me that my post didn't really answer the question of,
'So why is there a problem when I just run video through the VCR?' -- thanks
for the clarification. But clearly I was just plain wrong about where the
AGC! Do you know if there is any reason for the AGC to have such a slow
time constant other than to support Macrovision?
Making a digital backup is no problem, most stuff is digital these days,

For technically inclined people, yes. For the average consumer, we're not
quite at the point where most of them can easily duplicate their DVDs (DVD
burners have just become 'pretty darned cheap' in the past 3-6 months?), and
the studios are doing everything in their power to keep it annoying to do
so.
DVD players are much cheaper then VHS now.

Yep, fewer moving parts!

---Joel Kolstad
 
L

Luhan Monat

Jan 1, 1970
0
Joel said:
And do you happen to know why _this_ doesn't seriosuly mess up the PLL in
the TV and thereby distort the colors?

---Joel Kolstad
The TV uses the sync burst on each horizontal line to lock to the color
signal. If no burst signal is present it simply goes on at its present
prequency until the next one is found. VCR's, on the other hand, need
to sync to each line before recording them.

For a lot of information (public domain) look up Macrovision's patents
at USPTO.GOV - they also list patents on ways to defeat their system.
That way, they can go after companys that sell the decoding devices
under patent law.
 
J

Jan Panteltje

Jan 1, 1970
0
The TV uses the sync burst on each horizontal line to lock to the color
signal. If no burst signal is present it simply goes on at its present
prequency until the next one is found. VCR's, on the other hand, need
to sync to each line before recording them.
This is interesting, what do you mean by that?
Anyways in PAL the burst phase changes each line by 90 degrees,
if you omit a burst, chances are the 9.8 kHz (derived from the burst swing)
(h/2) is interrupted, and you get BW (color killer), although color killer
seems hardly used anymore.
Maybe NTSC world is simpler...
There is no technical reason why the VCR should need a NTSC burst each line,
the chroma is mixed with some frequency locked to H and then superimposed on the
FM carrier to the heads.
In playback that signal is taken from the heads before the FM limiter with a lowpass,
and mixed up again using a oscillator locked to H.
That way timing changes (as hor sync changes) are compensated in the final chroma.
(and you get right color).
So there must be an other reason for the color effect.
I looked up macrovision on that patent site, but no technical text of significance...
Maybe I missed it, can you be more specific about this?
Perhaps the chroma AGC in the VCR turns up the color a lot if a burst is missing,
burst is used for this gain control.
That would perhaps be possible.
JP
 
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