1 00:00:00,080 --> 00:00:03,989 When you hear the term “copy protection”, these days you’re probably more likely to 2 00:00:03,989 --> 00:00:08,960 think along the lines of DRM or some clever way to prevent copying a digital something-or-other, 3 00:00:08,960 --> 00:00:12,450 such as a music file, DVD, Blu-ray, or whatnot. 4 00:00:12,450 --> 00:00:15,940 If this is your frame of reference, you might be a little surprised to learn that a form 5 00:00:15,940 --> 00:00:21,520 of copy protection had been in use for pre-recorded video cassettes as far back as 1985. 6 00:00:21,520 --> 00:00:29,140 ♫ sweet music with tuba ♫ 7 00:00:33,620 --> 00:00:39,400 The Macrovision company, wh… which later became the Rovi corporation, which later bought 8 00:00:39,410 --> 00:00:44,680 TiVo and decided to absorb that identity so is now TiVo, came up with a way to exploit 9 00:00:44,680 --> 00:00:49,050 the automatic gain control circuitry in a videocassette recorder, and create pre-recorded 10 00:00:49,050 --> 00:00:53,660 tapes which would mess around with that circuitry to prevent copying them. 11 00:00:53,660 --> 00:00:58,190 Now to be clear, this wasn’t so much a copy protection scheme as it was a copy deterrent. 12 00:00:58,190 --> 00:01:00,520 This wouldn’t exactly prevent you from making a copy, 13 00:01:00,520 --> 00:01:03,800 but that copy would be almost unbearable to watch. 14 00:01:03,800 --> 00:01:05,260 So first let’s see what it does. 15 00:01:05,260 --> 00:01:10,080 I have this VCR plugged into this VCR, and the TV is currently displaying the output 16 00:01:10,080 --> 00:01:15,420 of this VCR through This VCR, and I’m gonna stick a prerecorded tape into this one and 17 00:01:15,420 --> 00:01:16,690 a blank tape into this one. 18 00:01:16,690 --> 00:01:19,030 I want to make a copy of Rain Main. 19 00:01:19,030 --> 00:01:23,341 So now, I’m going to hit record on this VCR, which will copy Rain Main onto the blank 20 00:01:23,341 --> 00:01:24,750 tape inside it. 21 00:01:24,750 --> 00:01:28,260 Pay attention to what happens as soon as I hit record. 22 00:01:32,660 --> 00:01:34,740 That’s not exactly a good sign. 23 00:01:34,750 --> 00:01:39,310 Well, aside from that, it seems to be working...OK, no apparent issues so far. 24 00:01:39,310 --> 00:01:42,870 But when you play the copy back, in addition to the generational loss brought about by 25 00:01:42,870 --> 00:01:48,170 being a second generation analog copy, the brightness of the image changes wildly, and 26 00:01:48,170 --> 00:01:49,750 it’s not at all stable. 27 00:01:49,750 --> 00:01:50,979 Why is that happening? 28 00:01:50,979 --> 00:01:52,890 And why only when I’m recording? 29 00:01:52,890 --> 00:01:57,000 Well, what Macrovision does is screw around with the vertical blanking interval of the 30 00:01:57,000 --> 00:02:01,890 video signal in such a way that a TV won’t really be bothered, but that a VCR attempting 31 00:02:01,890 --> 00:02:05,550 to record would incorrectly interpret as a change in signal strength. 32 00:02:05,550 --> 00:02:09,280 I’m not going to go too much into detail here, as I’ve already made a video explaining 33 00:02:09,280 --> 00:02:13,590 the basics of analog television, but at the start of every field there are a number of 34 00:02:13,590 --> 00:02:15,590 lines in the signal that are blank. 35 00:02:15,590 --> 00:02:19,910 They are transmitted at the highest intensity which creates a blacker than black segment 36 00:02:19,910 --> 00:02:24,580 that the TV can use to synchronize itself to a broadcast image and display it properly. 37 00:02:24,580 --> 00:02:28,020 To see the vertical blanking interval, you need to get yourself an old TV that allows 38 00:02:28,020 --> 00:02:29,900 you to adjust the vertical hold. 39 00:02:30,760 --> 00:02:33,420 This particular set to the rescue once more! 40 00:02:33,420 --> 00:02:37,420 I have the vertical hold ever so slightly off so the image will roll. 41 00:02:37,420 --> 00:02:41,910 This dark bar is the vertical blanking interval, and the really dark portion is the sync pulse 42 00:02:41,910 --> 00:02:43,810 that the TV is looking for. 43 00:02:43,810 --> 00:02:47,800 You can tell that it almost catches it each time it makes its way to the bottom, but with 44 00:02:47,800 --> 00:02:51,560 the adjustment just a tad off, it won’t stay in one place. 45 00:02:51,560 --> 00:02:55,680 Many videocassette recorders would use this pulse for determining the signal strength. 46 00:02:55,680 --> 00:02:59,370 Not all channels come in with the same strength, which in the land of video means they could 47 00:02:59,370 --> 00:03:02,840 appear brighter or darker depending on how clear the signal is coming in. 48 00:03:02,840 --> 00:03:08,420 A TV doesn’t care too much about the relative signal strength, but a VCR really does. 49 00:03:08,420 --> 00:03:13,170 Just like audio tape, a recording onto video tape needs to be made at the correct level. 50 00:03:13,170 --> 00:03:17,599 Too much saturation and detail is lost through clipping, and too little saturation and the 51 00:03:17,599 --> 00:03:19,040 picture becomes noisy. 52 00:03:19,040 --> 00:03:23,260 By calibrating its signal gain to the level of vertical blanking interval, the VCR would 53 00:03:23,260 --> 00:03:25,629 get a known reference point for brightness. 54 00:03:25,629 --> 00:03:29,360 This meant that no matter how strong the signal was or how bright or dark the scene it was 55 00:03:29,360 --> 00:03:33,640 recording was, a VCR would be able to make a recording correctly. 56 00:03:33,640 --> 00:03:37,400 So then, with this knowledge in their back pocket, Macrovision Solutions Corporation 57 00:03:37,400 --> 00:03:42,459 devised a way to mess with the blanking interval in order to confuse the gain control circuitry 58 00:03:42,459 --> 00:03:43,480 of a VCR. 59 00:03:43,480 --> 00:03:47,819 Let’s look at how Macrovision changed the blanking interval.This copy of the Magic School 60 00:03:47,819 --> 00:03:50,379 Bus wasn’t encoded with Macrovision. 61 00:03:50,379 --> 00:03:52,400 Notice how there’s really nothing in there. 62 00:03:52,400 --> 00:03:54,650 So what does a tape with macrovision look like? 63 00:03:54,650 --> 00:04:00,150 Well, with the Wrong Trousers, the BBC took care to encode their tape with Macrovision. 64 00:04:00,150 --> 00:04:02,900 Notice these new blocks inside the blanking interval. 65 00:04:02,900 --> 00:04:04,900 That IS Macrovision. 66 00:04:04,910 --> 00:04:08,830 You’ll see that next to the black blocks, which are actually high intensity pulses because 67 00:04:08,830 --> 00:04:13,190 a TV signal is inverted, are white blocks that keep fading in and out. 68 00:04:13,190 --> 00:04:16,810 This is likely what causes the brightness changes in the copied tape. 69 00:04:16,810 --> 00:04:20,749 A VCR that is recording this video signal keeps seeing the brightness of the vertical 70 00:04:20,749 --> 00:04:24,689 blanking interval go up and down, and it will treat it as though the entire signal were 71 00:04:24,689 --> 00:04:26,669 getting stronger or weaker. 72 00:04:26,669 --> 00:04:30,610 This means that it keeps erroneously adjusting the strength of the recording, which causes 73 00:04:30,610 --> 00:04:32,490 the recorded image to suffer. 74 00:04:32,490 --> 00:04:35,820 Warning: the following section of the video contains some speculation. 75 00:04:35,820 --> 00:04:38,110 OK, I ran into a wall regarding some specifics. 76 00:04:38,110 --> 00:04:43,529 A lot of the information about Macrovision you can find online seems incomplete and doesn’t 77 00:04:43,529 --> 00:04:45,779 really jive with what I’ve observed. 78 00:04:45,779 --> 00:04:49,800 Most descriptions of Macrovision will talk about the high intensity pulses and the automatic 79 00:04:49,800 --> 00:04:54,590 gain control, but this only explains the image getting brighter and darker. 80 00:04:54,590 --> 00:04:58,720 This might be particular to these two VCRs, but I tried dubbing in both directions and 81 00:04:58,720 --> 00:05:03,750 the resulting recordings were wildly unstable--not just too light or too dark. 82 00:05:03,750 --> 00:05:07,439 Because you can see the white blocks change in intensity when you look at the blanking 83 00:05:07,439 --> 00:05:11,669 interval, it would seem that this is what causes the image to go light and dark. 84 00:05:11,669 --> 00:05:12,669 And that’s fine. 85 00:05:12,669 --> 00:05:16,759 But in addition to these pulses, which are described as “excessive voltage pulses”, 86 00:05:16,759 --> 00:05:18,840 there’s a little something else. 87 00:05:18,840 --> 00:05:23,259 These handy oscilloscope captures on the Wikipedia page show that the intensity of the high voltage 88 00:05:23,259 --> 00:05:27,469 spike goes up and down, and the lower portion here stays constant. 89 00:05:27,469 --> 00:05:31,610 So this means that this part is the white boxes we can see appear and disappear. 90 00:05:31,610 --> 00:05:35,869 Assuming these two graphs show these two states of the vertical blanking interval, then the 91 00:05:35,869 --> 00:05:39,830 only component that changes is the level of these upper pulses. 92 00:05:39,830 --> 00:05:43,129 This make sense because the light portion follows a dark portion. 93 00:05:43,129 --> 00:05:45,330 Within the lines, you can see dark, light, grey. 94 00:05:45,330 --> 00:05:46,460 Dark, light, grey. 95 00:05:46,460 --> 00:05:50,560 And the graph does the same--dark light grey, dark light grey. 96 00:05:50,560 --> 00:05:54,850 I think that not enough attention is given to these lower pulses, as these appear to 97 00:05:54,850 --> 00:05:59,409 be at the same level as the synchronization pulse in the vertical blanking interval. 98 00:05:59,409 --> 00:06:03,309 If we go back to the tape without Macrovision, you can see this very dark portion here in 99 00:06:03,309 --> 00:06:04,310 the blanking interval. 100 00:06:04,310 --> 00:06:08,930 That is the high intensity pulse that the TV locks onto for vertical synchronization. 101 00:06:08,930 --> 00:06:11,520 But the rest of the blanking interval is just a grey color. 102 00:06:11,520 --> 00:06:13,060 That’s just the black level. 103 00:06:13,060 --> 00:06:16,650 Many black and white televisions including this one can’t produce a true black unless 104 00:06:16,650 --> 00:06:20,340 there’s a good deal of contrast in the scene, which is why it appears grey. 105 00:06:20,340 --> 00:06:23,960 It will however always produce true black during the sync pulse, because that pulse 106 00:06:23,960 --> 00:06:27,899 is blacker than black--meaning the electron gun is entirely shut off. 107 00:06:27,899 --> 00:06:32,289 When you go back to the tape with Macrovision, you can see that the added black bars are 108 00:06:32,289 --> 00:06:34,970 also at that blacker than black intensity. 109 00:06:34,970 --> 00:06:39,449 It seems to me that these probably screw around with a VCR’s ability to maintain vertical 110 00:06:39,449 --> 00:06:40,830 synchronization. 111 00:06:40,830 --> 00:06:45,259 These dark boxes extend the sync pulse farther into the blanking interval than it should 112 00:06:45,259 --> 00:06:48,879 be, and the pulses appear multiple times within a single line. 113 00:06:48,879 --> 00:06:52,080 The white bars that appear and disappear are likely what interferes with the automatic 114 00:06:52,080 --> 00:06:55,939 gain control and will cause the brightness issues, but that shouldn’t mess with tracking 115 00:06:55,939 --> 00:06:57,550 or image stability. 116 00:06:57,550 --> 00:07:00,530 There seems to be more than just that going on. 117 00:07:00,530 --> 00:07:05,189 Some descriptions of Macrovision call dubbed tapes simply annoying to watch, but this? 118 00:07:05,189 --> 00:07:06,610 This is unwatchable. 119 00:07:06,610 --> 00:07:10,229 Just to check that it wasn’t simply this TV that was struggling to maintain synchronization 120 00:07:10,229 --> 00:07:14,830 from the copied tape, I played the tape back through the LCD TV in my kitchen, which doesn’t 121 00:07:14,830 --> 00:07:19,039 use the vertical blanking interval in quite the same way a CRT television does. 122 00:07:19,039 --> 00:07:23,639 It had a more stable image, but not only did the image repeatedly become darker, it lost 123 00:07:23,639 --> 00:07:28,599 all color completely and the VCR was clearly struggling to maintain tracking. 124 00:07:28,599 --> 00:07:31,660 You can hear the pitch of the audio waver continuously. 125 00:07:31,660 --> 00:07:36,162 ♫ severely warbled music ♫ 126 00:07:36,162 --> 00:07:40,220 The signal got so bad that the TV kept blanking the screen and giving up. 127 00:07:40,220 --> 00:07:44,509 It seems possible to me that not only does Macrovision mess with the automatic gain control, 128 00:07:44,509 --> 00:07:48,449 but it might also mess with automatic tracking circuits of a VCR. 129 00:07:48,449 --> 00:07:51,449 Which may help to partially explain the next part: 130 00:07:51,449 --> 00:07:56,259 Regardless of the exact specifics of Macrovision, there’s one interesting quirk to the system. 131 00:07:56,259 --> 00:08:00,499 Really old VCRs, which don’t have the same automatic gain control circuitry of their 132 00:08:00,499 --> 00:08:03,909 modern counterparts, are impervious to Macrovision. 133 00:08:03,909 --> 00:08:08,089 (every time I need to move this thing, I regret it.) 134 00:08:08,089 --> 00:08:12,270 This beast just really doesn’t care what’s going on in the vertical blanking interval. 135 00:08:12,270 --> 00:08:14,389 It will dub that tape just fine for ya. 136 00:08:14,389 --> 00:08:17,659 See, it’s recording right now, and the TV doesn’t show anything weird. 137 00:08:17,660 --> 00:08:19,940 Let’s play the copy back to be sure. 138 00:08:19,940 --> 00:08:21,960 Yep, just fine. 139 00:08:22,680 --> 00:08:24,280 Hey, it’s me from the future. 140 00:08:24,289 --> 00:08:28,169 While shooting the B-roll I needed for this video, I noticed that the VCR which was copying 141 00:08:28,169 --> 00:08:32,029 Rain Man was making really odd sounds as it recorded. 142 00:08:32,029 --> 00:08:34,340 Take a listen. 143 00:08:35,180 --> 00:08:44,780 [sound of VCR recording but with wild speed fluctuations] 144 00:08:46,220 --> 00:08:50,880 Normally you never hear a VCR make noises like this, except for maybe when it’s adjusting 145 00:08:50,880 --> 00:08:52,350 its tracking. 146 00:08:52,350 --> 00:08:56,210 This really seems like the Macrovision is confusing the VCR on where the start of the 147 00:08:56,210 --> 00:09:00,550 video field actually is, and it keeps trying to compensate for that. 148 00:09:00,550 --> 00:09:04,900 The video head drum needs to spin in perfect alignment with the video signal, and it seems 149 00:09:04,900 --> 00:09:09,780 like this VCR is being fooled into thinking the start of each frame moves as the macrovision 150 00:09:09,780 --> 00:09:11,510 blocks fade in and out. 151 00:09:11,510 --> 00:09:16,460 The old VCR probably isn’t affected because it doesn’t try to chase a wavering signal-- 152 00:09:16,460 --> 00:09:20,420 I would imagine it has much less of an ability to adjust the speed of its video head and 153 00:09:20,420 --> 00:09:25,460 tape transport to signal fluctuations, and as a result Macrovision just doesn’t affect it. 154 00:09:25,460 --> 00:09:26,440 Anyway, 155 00:09:26,440 --> 00:09:30,460 Even into the days of Macrovision, there were some VCRs that weren’t affected by it. 156 00:09:30,460 --> 00:09:35,170 It was estimated that 85% were, but that leaves a significant number of VCRs floating around 157 00:09:35,170 --> 00:09:36,870 which just don’t care about it. 158 00:09:36,870 --> 00:09:40,790 Also, for those that were so inclined, getting a Macrovision defeat device from the grey 159 00:09:40,790 --> 00:09:42,710 market wasn’t all that hard. 160 00:09:42,710 --> 00:09:45,280 In fact, you could build one yourself. 161 00:09:45,280 --> 00:09:49,670 Because Macrovision can’t entirely eliminate the pulse for vertical synchronization, otherwise 162 00:09:49,670 --> 00:09:54,400 the TV couldn’t display an image at all, a defeat device just needs to remove the altered 163 00:09:54,400 --> 00:09:58,360 parts that were messed up with the boxes and replace it with standard black lines. 164 00:09:58,360 --> 00:10:02,620 Now, when DVD came along, Macrovision was incorporated here, too. 165 00:10:02,620 --> 00:10:06,750 Because DVDs are a digital format, they don’t contain the video fields like a videocassette 166 00:10:06,750 --> 00:10:10,461 does, so the player actually generates the Macrovision in the vertical blanking interval 167 00:10:10,461 --> 00:10:12,300 of its composite output. 168 00:10:12,300 --> 00:10:16,470 It will only do it so long as the disc asks for it, which not all of them did. 169 00:10:16,470 --> 00:10:20,690 For example, this copy of the Princess Bride doesn’t use Macrovision, but this copy of 170 00:10:20,690 --> 00:10:22,260 Spirited Away does. 171 00:10:22,260 --> 00:10:26,330 The fact that the analog Macrovision system was shoved into the DVD format caused some 172 00:10:26,330 --> 00:10:28,840 problems for early DVD adopters. 173 00:10:28,840 --> 00:10:32,220 Remember how the image got messed up only after I had hit record? 174 00:10:32,220 --> 00:10:36,090 That happened because unless it’s recording, the automatic gain control circuitry isn’t 175 00:10:36,090 --> 00:10:39,430 active and it passes the signal straight through to the TV. 176 00:10:39,430 --> 00:10:44,640 But many VCRs weren’t so kind and instead applied automatic gain control to whatever 177 00:10:44,640 --> 00:10:48,500 input they received, regardless of if it was recording or not. 178 00:10:48,500 --> 00:10:53,361 Many TVs only had one composite input, so for anyone who hooked their new DVD player 179 00:10:53,361 --> 00:10:58,500 into their TV through their VCR, and if their VCR didn’t simply pass-through the video 180 00:10:58,500 --> 00:11:01,820 from the DVD player, they might get a horrible mess. 181 00:11:01,820 --> 00:11:05,860 Imagine how annoying it would be to play your first DVD and all of the sudden have the image 182 00:11:05,860 --> 00:11:07,590 come out like that. 183 00:11:07,590 --> 00:11:11,680 Many people thought their new DVD players were somehow broken, but thankfully newer 184 00:11:11,680 --> 00:11:17,150 VCRs like this one won’t cause a fuss unless you tried to record from the DVD player. 185 00:11:17,150 --> 00:11:21,180 And while we’re at it, this attempted copying of Spirited Away shows a second thing added 186 00:11:21,180 --> 00:11:24,920 to Macrovision, which was called Level II ACP. 187 00:11:24,920 --> 00:11:28,640 This would invert the phase of the colorburst occasionally, which produced stripes of the 188 00:11:28,640 --> 00:11:30,800 wrong color on a copy. 189 00:11:30,800 --> 00:11:34,280 Quite honestly that’s the least annoying of the issues with this recording. 190 00:11:34,280 --> 00:11:38,330 Now these days, far more complicated copy protection schemes are in use, much to the 191 00:11:38,330 --> 00:11:43,080 chagrin of anyone who wants to make legal copies of their media which is, by the way, 192 00:11:43,080 --> 00:11:44,040 allowed. 193 00:11:44,040 --> 00:11:46,920 But Macrovision was I think quite clever. 194 00:11:46,920 --> 00:11:50,880 By messing with the fundamental structure of the video signal just enough to keep a 195 00:11:50,880 --> 00:11:57,250 recording VCR from working correctly, but not enough for a TV or a playing to become 196 00:11:57,250 --> 00:12:00,120 confused, they actually had a pretty elegant solution. 197 00:12:00,120 --> 00:12:02,480 Thanks for watching, I hoped you enjoyed the video! 198 00:12:02,480 --> 00:12:05,620 If this is your first time coming across the channel and you liked what you saw, please 199 00:12:05,620 --> 00:12:07,660 subscribe to Technology Connections! 200 00:12:07,660 --> 00:12:09,580 You can also support the channel on Patreon. 201 00:12:09,580 --> 00:12:12,880 Patrons of the channel are what keeps these videos coming, and if you’d like to join 202 00:12:12,880 --> 00:12:16,940 the awesome people who make this possible, please check out my Patreon page. 203 00:12:16,940 --> 00:12:19,140 Thanks for your consideration, and I’ll see you next time!