> The pattern across any single frame is entirely random noise.

This is untrue in at least one sense. The patterning within the animated letters cycles. It is generated either by evaluating a periodic function or by reading from a file using a periodic offset.

Can't it be continuous random noise added at the top and then moved down each frame.

Roughly you create another full size rect. On each frame add a random pixel on row 1 and shift everything down.

Make that rest a layer below the top one which has Hello cut out as transparent.

In any single frame the result is random noise.

You could do that, but that's not what the page is doing.

You don't even need to maintain the approach of having the pattern within the text move downwards over time. You could redraw it every frame with random data, as if it was television static. It would still be easy to read, as long as the background stayed fixed.

They didn't mean random noise as in certifiably truly random in a cryptographic sense... nobody cares about that for a silly demo.

Random noise as in a normal non-tech human cannot see anything discernable to them at all, without the motion component.

Hah, late reply, but as a generative artist, the True Randomness in Computing rabbit hole has no perceivable bottom.

As you said, I was _not_ alluding to more than being perceivably random/noisy.