How to create this transition effect?

[Blaise Douros]

Here’s what it looks like to me:

There are two of elements being used here: first, the lower-left-to-upper-right lines (LLTUR), which are building a solid matte to reveal the image, and second, the “decorative” motion elements which consist of the circular moving lines and the upper-right-to-lower-left ones.

The classroom itself looks like a static image, possibly pre-built and rendered as a PNG, though I have another theory about it, too. The floor line is a simple stroke effect.

Creating the LLTUR lines for the matte reveal of the classroom is probably being done in a simple shape layer with repeaters. This tutorial gives a pretty good overview: https://lesterbanks.com/2020/01/how-to-create-grids-with-a-shape-layer-repeater/

In this case, instead of creating a grid, you’d be using it to create a white-to-black matte with the LLTUR lines building up over time, and then using it as a luma matte to composite the classroom into place.

As for the decorative elements, I’m not sure what method is being used to color match them to the regions in which they end up, but they are likely created with similar methods.

[Chad Ridgeway]

I like the theory but does repeater have that sort of randomization that those rectangle bars are using to draw on ?

[Filip Vandueren]

After the repeater Add a “Wiggle Transform” for which you animate the position.

[Blaise Douros]

You can create the repeated lines with a variety of spatial offsets and/or use multiple copies to accomplish the randomized look. You’ll notice they’re all moving at the same speed, they’re just starting in different places.