When you hear the term “copy protection”,
these days you’re probably more likely to think along the lines of DRM or some clever
way to prevent copying a digital something-or-other, such as a music file, DVD, Blu-ray, or whatnot. If this is your frame of reference, you might
be a little surprised to learn that a form of copy protection had been in use for pre-recorded
video cassettes as far back as 1985. ♫ sweet music with tuba ♫ The Macrovision company, wh… which later
became the Rovi corporation, which later bought TiVo and decided to absorb that identity so
is now TiVo, came up with a way to exploit the automatic gain control circuitry in a
videocassette recorder, and create pre-recorded tapes which would mess around with that circuitry
to prevent copying them. Now to be clear, this wasn’t so much a copy
protection scheme as it was a copy deterrent. This wouldn’t exactly prevent you from making
a copy, but that copy would be almost unbearable to watch. So first let’s see what it does. I have this VCR plugged into this VCR, and
the TV is currently displaying the output of this VCR through This VCR, and I’m gonna
stick a prerecorded tape into this one and a blank tape into this one. I want to make a copy of Rain Main. So now, I’m going to hit record on this
VCR, which will copy Rain Main onto the blank tape inside it. Pay attention to what happens as soon as I
hit record. That’s not exactly a good sign. Well, aside from that, it seems to be working...OK,
no apparent issues so far. But when you play the copy back, in addition
to the generational loss brought about by being a second generation analog copy, the
brightness of the image changes wildly, and it’s not at all stable. Why is that happening? And why only when I’m recording? Well, what Macrovision does is screw around
with the vertical blanking interval of the video signal in such a way that a TV won’t
really be bothered, but that a VCR attempting to record would incorrectly interpret as a
change in signal strength. I’m not going to go too much into detail
here, as I’ve already made a video explaining the basics of analog television, but at the
start of every field there are a number of lines in the signal that are blank. They are transmitted at the highest intensity
which creates a blacker than black segment that the TV can use to synchronize itself
to a broadcast image and display it properly. To see the vertical blanking interval, you
need to get yourself an old TV that allows you to adjust the vertical hold. This particular set to the rescue once more! I have the vertical hold ever so slightly
off so the image will roll. This dark bar is the vertical blanking interval,
and the really dark portion is the sync pulse that the TV is looking for. You can tell that it almost catches it each
time it makes its way to the bottom, but with the adjustment just a tad off, it won’t
stay in one place. Many videocassette recorders would use this
pulse for determining the signal strength. Not all channels come in with the same strength,
which in the land of video means they could appear brighter or darker depending on how
clear the signal is coming in. A TV doesn’t care too much about the relative
signal strength, but a VCR really does. Just like audio tape, a recording onto video
tape needs to be made at the correct level. Too much saturation and detail is lost through
clipping, and too little saturation and the picture becomes noisy. By calibrating its signal gain to the level
of vertical blanking interval, the VCR would get a known reference point for brightness. This meant that no matter how strong the signal
was or how bright or dark the scene it was recording was, a VCR would be able to make
a recording correctly. So then, with this knowledge in their back
pocket, Macrovision Solutions Corporation devised a way to mess with the blanking interval
in order to confuse the gain control circuitry of a VCR. Let’s look at how Macrovision changed the
blanking interval.This copy of the Magic School Bus wasn’t encoded with Macrovision. Notice how there’s really nothing in there. So what does a tape with macrovision look
like? Well, with the Wrong Trousers, the BBC took
care to encode their tape with Macrovision. Notice these new blocks inside the blanking
interval. That IS Macrovision. You’ll see that next to the black blocks,
which are actually high intensity pulses because a TV signal is inverted, are white blocks
that keep fading in and out. This is likely what causes the brightness
changes in the copied tape. A VCR that is recording this video signal
keeps seeing the brightness of the vertical blanking interval go up and down, and it will
treat it as though the entire signal were getting stronger or weaker. This means that it keeps erroneously adjusting
the strength of the recording, which causes the recorded image to suffer. Warning: the following section of the video
contains some speculation. OK, I ran into a wall regarding some specifics. A lot of the information about Macrovision
you can find online seems incomplete and doesn’t really jive with what I’ve observed. Most descriptions of Macrovision will talk
about the high intensity pulses and the automatic gain control, but this only explains the image
getting brighter and darker. This might be particular to these two VCRs,
but I tried dubbing in both directions and the resulting recordings were wildly unstable--not
just too light or too dark. Because you can see the white blocks change
in intensity when you look at the blanking interval, it would seem that this is what
causes the image to go light and dark. And that’s fine. But in addition to these pulses, which are
described as “excessive voltage pulses”, there’s a little something else. These handy oscilloscope captures on the Wikipedia
page show that the intensity of the high voltage spike goes up and down, and the lower portion
here stays constant. So this means that this part is the white
boxes we can see appear and disappear. Assuming these two graphs show these two states
of the vertical blanking interval, then the only component that changes is the level of
these upper pulses. This make sense because the light portion
follows a dark portion. Within the lines, you can see dark, light,
grey. Dark, light, grey. And the graph does the same--dark light grey,
dark light grey. I think that not enough attention is given
to these lower pulses, as these appear to be at the same level as the synchronization
pulse in the vertical blanking interval. If we go back to the tape without Macrovision,
you can see this very dark portion here in the blanking interval. That is the high intensity pulse that the
TV locks onto for vertical synchronization. But the rest of the blanking interval is just
a grey color. That’s just the black level. Many black and white televisions including
this one can’t produce a true black unless there’s a good deal of contrast in the scene,
which is why it appears grey. It will however always produce true black
during the sync pulse, because that pulse is blacker than black--meaning the electron
gun is entirely shut off. When you go back to the tape with Macrovision,
you can see that the added black bars are also at that blacker than black intensity. It seems to me that these probably screw around
with a VCR’s ability to maintain vertical synchronization. These dark boxes extend the sync pulse farther
into the blanking interval than it should be, and the pulses appear multiple times within
a single line. The white bars that appear and disappear are
likely what interferes with the automatic gain control and will cause the brightness
issues, but that shouldn’t mess with tracking or image stability. There seems to be more than just that going
on. Some descriptions of Macrovision call dubbed
tapes simply annoying to watch, but this? This is unwatchable. Just to check that it wasn’t simply this
TV that was struggling to maintain synchronization from the copied tape, I played the tape back
through the LCD TV in my kitchen, which doesn’t use the vertical blanking interval in quite
the same way a CRT television does. It had a more stable image, but not only did
the image repeatedly become darker, it lost all color completely and the VCR was clearly
struggling to maintain tracking. You can hear the pitch of the audio waver
continuously. ♫ severely warbled music ♫ The signal got so bad that the TV kept blanking
the screen and giving up. It seems possible to me that not only does
Macrovision mess with the automatic gain control, but it might also mess with automatic tracking
circuits of a VCR. Which may help to partially explain the next
part: Regardless of the exact specifics of Macrovision,
there’s one interesting quirk to the system. Really old VCRs, which don’t have the same
automatic gain control circuitry of their modern counterparts, are impervious to Macrovision. (every time I need to move this thing, I regret
it.) This beast just really doesn’t care what’s
going on in the vertical blanking interval. It will dub that tape just fine for ya. See, it’s recording right now, and the TV
doesn’t show anything weird. Let’s play the copy back to be sure. Yep, just fine. Hey, it’s me from the future. While shooting the B-roll I needed for this
video, I noticed that the VCR which was copying Rain Man was making really odd sounds as it
recorded. Take a listen. [sound of VCR recording but with wild speed fluctuations] Normally you never hear a VCR make noises
like this, except for maybe when it’s adjusting its tracking. This really seems like the Macrovision is
confusing the VCR on where the start of the video field actually is, and it keeps trying
to compensate for that. The video head drum needs to spin in perfect
alignment with the video signal, and it seems like this VCR is being fooled into thinking
the start of each frame moves as the macrovision blocks fade in and out. The old VCR probably isn’t affected because
it doesn’t try to chase a wavering signal-- I would imagine it has much less of an ability
to adjust the speed of its video head and tape transport to signal fluctuations, and
as a result Macrovision just doesn’t affect it. Anyway, Even into the days of Macrovision, there were
some VCRs that weren’t affected by it. It was estimated that 85% were, but that leaves
a significant number of VCRs floating around which just don’t care about it. Also, for those that were so inclined, getting
a Macrovision defeat device from the grey market wasn’t all that hard. In fact, you could build one yourself. Because Macrovision can’t entirely eliminate
the pulse for vertical synchronization, otherwise the TV couldn’t display an image at all,
a defeat device just needs to remove the altered parts that were messed up with the boxes and
replace it with standard black lines. Now, when DVD came along, Macrovision was
incorporated here, too. Because DVDs are a digital format, they don’t
contain the video fields like a videocassette does, so the player actually generates the
Macrovision in the vertical blanking interval of its composite output. It will only do it so long as the disc asks
for it, which not all of them did. For example, this copy of the Princess Bride
doesn’t use Macrovision, but this copy of Spirited Away does. The fact that the analog Macrovision system
was shoved into the DVD format caused some problems for early DVD adopters. Remember how the image got messed up only
after I had hit record? That happened because unless it’s recording,
the automatic gain control circuitry isn’t active and it passes the signal straight through
to the TV. But many VCRs weren’t so kind and instead
applied automatic gain control to whatever input they received, regardless of if it was
recording or not. Many TVs only had one composite input, so
for anyone who hooked their new DVD player into their TV through their VCR, and if their
VCR didn’t simply pass-through the video from the DVD player, they might get a horrible
mess. Imagine how annoying it would be to play your
first DVD and all of the sudden have the image come out like that. Many people thought their new DVD players
were somehow broken, but thankfully newer VCRs like this one won’t cause a fuss unless
you tried to record from the DVD player. And while we’re at it, this attempted copying
of Spirited Away shows a second thing added to Macrovision, which was called Level II
ACP. This would invert the phase of the colorburst
occasionally, which produced stripes of the wrong color on a copy. Quite honestly that’s the least annoying
of the issues with this recording. Now these days, far more complicated copy
protection schemes are in use, much to the chagrin of anyone who wants to make legal
copies of their media which is, by the way, allowed. But Macrovision was I think quite clever. By messing with the fundamental structure
of the video signal just enough to keep a recording VCR from working correctly, but
not enough for a TV or a playing to become confused, they actually had a pretty elegant
solution. Thanks for watching, I hoped you enjoyed the
video! If this is your first time coming across the
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