How to add pixel grid to video?

Question

Design

Good day!
I need to make a video for the project for the header. Everything I need I can do in Sony Vegas, except for one thing. I don't know how to add pixel grid to video. Here is a link where it is implemented -
panoptiqm.com/#Gooses_Weekend-137
If you look closely, the picture seems to be all made up of squares. Here is what I want to achieve.
The technology itself is not new, but I can't find how it's done. If anyone knows, I would be grateful for the answer, but someone knows for sure!
So thanks!)

Answer 1

Video on background + absolute div with background - panoptiqm.com/img/pattern.png
Well, you can play around with opacity.