How to achieve the "magic swipe" effect in this video?

Question

How to achieve the "magic swipe" effect in this video (at 0:16)?

https://www.facebook.com/diplycrafty/videos/1867777256617888/

Is it necessary to use After Effects? Can other open source software do so too?

Answer 1

Assuming you're using a layer based compositor (like After Effects) you need two layers. The top layer has the half-painted box with the hand swiping over it. The bottom has the fully painted box, and no hand, but everything else is the same as the first shot.

Now you need to make a matte that corresponds to the trailing edge of the hand, and extending (roughly) to the the top left of the screen and down the left side. As the hand moves across this matte will follow it, so that at the start it is not over the box, and at the end it completly covers it. the easiest way to do this would be to trace the hand, but there are other ways like rotobrush in After Effects. Apply this matte to the top layer so that it hides everything inside it.

Alternatively you could shoot the hand over a green background and use chroma keying to remove the background. Then use a simple matte to reveal the painted box, with the transition hidden by the hand layer. You could even get away with a single still image of the hand, animated to look like it was moving, if the movement is fast and simple enough.

It's certainly doable with After Effects, but You could use Blender or any compositor or NLE that has the capability to create moving mattes