Those are
frightfully well done. You don't even see
any blurs, pixelations, lighting flaws or other discontinuities. Especially in the first two. I'm sure a bit of it was the clever use of editing, putting mask or whatever on a few frames where the head wasn't in shot anyway, but even that could have left traces - but didn't leave any I could spot. Damn, this
is a bit scary. That scene from
When Harry met Sally, the one from
Pretty Woman, and especially that shot where the dude in the tux meets the lady in the ball-gown. Even the people moving in the background, where her head would have been, looked entirely flawless.
Damn. I've seen Stalin-era photos, which professional craftsmen spent hours and hours, or more likely days and weeks on, to remove Trotski, entirely analog, that didn't look half as convincing as this stuff. Yes, no blood, and the stumps didn't look particularly biological, either, but that's beside the point. I was aware that such fakery is possible these days. Even to such a degree of perfection. But that it's apparently so simple and affordable that someone can do it for some inconsequential youtube videos ... unless it's some sort of showreel. But they rarely make a whole series out of those, do they? Unless whoever made these wants to demonstrate how quick they can work.
The website doesn't look like it, I don't see any advertisement of digital-sfx services.
Perhaps it's not quite as convincing if you view it frame by frame in high res, I think there might be a tiny blur and not entirely correct movement of a head in the background in one shot from pretty woman, he's got some large animated gifs on his website. But I'm not certain, I may well just be imagining it there.