It's a system that's supposed to make it harder to make copies of pre-recorded video tapes and discs, though it does nothing of the sort. Anybody who wants to copy a Macrovision protected film, can easily do so. One thing that it does do, though; is make it next to impossible to watch Macrovision protected recordings on many TV sets (the picture can roll and flicker, very badly).
Macrovision works by inserting non-standard and “illegal” signals into the video signal (illegal meaning the specifications that video signals that are required to be adhered to, are being deliberately violated). Therein lays the problem; as most video equipment (that's designed properly) is designed to work with standard video signals. If you give them non-standard signals, their reaction is unpredictable.
It's only supposed to upset VCRs (which tend to be more fussy about the signals they can use than TV sets), but it also upsets many TVs. And many people still have TV sets without video input sockets, or only has one set of inputs; so they try connecting their DVD player through their VCR, which mayn't handle the Macrovision signal, and their VCR corrupts it before passing it on to the TV set. But if the DVD player had an RF output, that you could connect directly to the TV set, the TV might have accepted the signal.
Buy another TV set that has direct video inputs, and doesn't mind Macrovision. But that's expensive. And how do you test it, before purchase?
Buy another DVD player that doesn't support Macrovision, if you can find one.
Find a crack for your DVD player that disables Macrovision (a set-up code, or physical modification to the player), though not all can be cracked.
Dump your DVD player, and forget about it (as I've seen people do).
Buy a video processing device for defeating Macrovision.
The last one is probably the easiest to implement. You can use it with any video source that gives you Macrovision problems (it's not just DVDs that have Macrovision signals on them, many pre-recorded video tapes also have it). It gives you one solution for all of the potential problem devices. Particularly as it's next to impossible to modify a VCR to overcome Macrovision (pre-recorded tapes that are protected with Macrovision, are recorded with it as a part of the video signal; but for DVDs, they have a code that tells the player to add Macrovision to the video signal, and that instruction can sometimes be disabled). And doesn't involve modifying your player, which may void your warrentee.
But modifying your DVD player, is the most convenient. Once “fixed,“ you'd be able to use the player with any TV or VCR, without any problems, and without having to cart another box around with you.
It can do one, or more, of several things to the video signal. Here's the ones that I know about:
Mess up the video signal just before the vertical sync, at the very bottom of the picture; causing lack of vertical lock (the picture may jitter up and down), and causing horizontal juddering at the top of of the picture.
Mess up the video signal just after the vertical sync, just above the start of the picture; causing the picture contrast and/or brightness to progressively vary, and rapidly flash at you. You can see this signal, if you have a projection screen TV; or if you roll the vertical sync, so that the picture is half way down the screen. It looks like a black and white check pattern, that changes brightness slowly and rapidly, in an annoying sequence. And, as these black and white checks go above and below the legal video signal levels, they can cause problems for signals passing through RF modulators, making an annoying buzzing on the sound.
Mess up the colour sub-carrier; causing the colour to flicker, or drop out completely.
The second one is what causes most people problems. The others generally don't create noticeable problems while watching a Macrovisioned signal, but will if you try to record one. Fixing up the second one, will usually be enough so that you can watch films without aggrevation.
Technically, the solution is quite simple:
To fix up the most common problem, you run the signal through a processor that strips out any signals between the vertical sync and the start of the picture. Simply removing the extraneous rubbish, is enough to fix viewing most Macrovisioned signals; as Macrovision is making an addition to a standard signal, not a modification of it. Re-inserting the "vertical blanking period," takes care of the main problem.
“Sync-restorers” and “video stabilisers” could probably fix the errors introduced both before and after the vertical sync period, though they're usually designed to cope with normal or damaged signals, not deliberately illegal ones. They often can re-insert vertical blanking, too.
Such devices are a standard part of many professional video equipment (known as a “proc amp,” as an abbreviation for a “processing amplifier”), as a common way of handling video signals from different sources (e.g. signals that have been damaged along the way, or just to match signal levels with the rest of the equipment).
They're often available as stand-alone devices, sometimes quite cheaply, as a video hobbyist device, or a do-it-yourself kit of parts. Jaycar (an electronics retail chain in Australia) sells such a kit, called “Dr Video”. It's quite simple to build, and really only requires basic soldering skills. I've built one, and reviewed it on this website. Also check out any video hobbyist magazines for advertisements for pre-built units.
Digital Megahouse (formerly City South Electronics Pty Ltd) sells a prebuilt video stabiliser device. I've not seen it in action, but received an e-mail about it, and chatted with the vendor about them (when they were City South Electronics); so I've included a link to it, to help people annoyed at not being able to watch their own DVDs, but don't want to have to build their own de-macrovision gadget. Of course, given the chance to review one, I will.