Last night, Derren Brown did a rather excellent stunt where he appeared to have predicted the results of the National Lottery draw.
I can't tell you how he did it, but I can tell you how I'd do it. If you don't want to know, don't read. Bear in mind I've never tried this, so I've not had that chance to work out the fine details.
The whole thing was shot with no audience and two cameras, which is one more camera and one fewer audience than I'd use if it was real, and one of the cameras (which I'll call 'camera 2') was needlessly far away. (The camera that follows Derren into the studio I shall obviously call 'camera 1'.)
So. Derren walks in, followed by camera 1. He gives his spiel, pointing out camera 2, strides over to the podium and TV, waves to camera 2, which gets some nice wide-shots of the setup. Then everyone breaks for tea.
Next, top-secret camera 3 is mounted on a tracking device, similar to the ones that power those ever-so-precise spotlights that spin around so impressively on Who Wants To Be A Millionaire?. It films the podium of balls for 10 minutes while nothing happens. (You could reuse camera 2, but for clarity I'm invoking a third.)
At precisely the same moment, shortly before broadcast, the video of the balls camera 3 took starts rolling in the editing room, and the same sequence of moves is started on the live camera so that the two feeds perfectly match up. This means the editor can cut between the pre-recorded balls and the live feed seamlessly.
When broadcast starts, camera 1 and Derren are in the next room. He then walks in, and camera 1 follows him. You cut in a shot taken with camera 2 earlier in the day (with live sound), which falsely establishes that (a) there is a second camera at the back of the room, and (b) there are no other cameras, and no clever moving camera mounts. You can't tell camera 2 isn't live because it's too brief and far away to show lip-sync in detail. Now you have to get from the live camera 1 feed to the live camera 3 feed without an obvious cut. So camera 1 is held next to the mounting device, and Derren waves to the back of the room, where camera 2 used to be. This is an excuse to cut to another pre-recorded wide-shot. Partway through the wave (nice touch) you cut 'back' to the live camera 3 feed. From here on, the camera rotates and zooms slightly, but never moves, and the whole thing can go out live until the draw starts.
At this point, while all eyes are fixed on Derren or the podium, Andy Nyman robs a bank. Remember that this was billed as a feat of misdirection.
Meanwhile, back in the studio, Derren moves round to the other side of the TV, so nothing is anywhere near the podium with the balls. This allows the editor to cut in the left hand side of the image from the pre-recorded footage, masking somebody quietly taking out the dummy balls and putting in the correct ones, as they're drawn. The edge of this mask is smooth, because a crisp join is obvious even when it's perfectly done. When the balls are in place, you quickly fade out the pre-recorded mask. (With luck, camera motion will mask this.) Once you're back totally live, Derren triumphantly walks over to the podium, and the program on camera 3 switches to a predefined 'zoom in on the balls' sequence.
I'm pretty convinced this is how he did it too, because the whole broadcast plays out how I'd expect it to. But I obviously wanted to get this out there before tomorrow's show.
On other hands, I've heard a theory that camera 3 was fixed and the motion is a computer effect, which is equally plausible. It'd be more robust to things going wrong but probably less convincing if they don't. I'm told if you look carefully you can see the screen-left ball jump slightly, but I don't think the YouTube version above shows that clearly. I've also heard a lot of people whine about freezes and balls with ambiguous numbers (including, at one stage, a ball 59) and so forth. I've even seen one person complain that the camera motion froze momentarily who believed it was a computer effect.
It's fascinating to me that the same fallacious 'flaws' people imagine in the moon landing videos are also applied to this kind of thing, which genuinely is fake and is therefore by definition already plausibly fake without inventing extra reasons. You want proof it's fake? It's a video of a man predicting a lottery draw. If that's not enough for you then there's something wrong.