> I dropped it in the end partly because of all the problems and edge cases, partly because its a solution looking for a problem an AI essentially wipes out any demand for generating video in browsers.

That is only because your view omits some other problems this solves/products this enables.

There is an incredible ecosystem of tools out the browser land, to create animation.

If you can capture frames from the browser you can render these animations as videos, with motion blur (render 2500 frame for a second of video, blend 100 frames each with a shutter function) to get 25fps with 100 motion blur samples (a number AfterEffects can't do, e.g).

There’s a tiny, tiny market for people who would pay for this.

Also you must understand that chrome is not a deterministic renderer. You cannot get the per frame control because it is fundamentally designed to get frames in front of the user fast.

They did some work around the concept of virtual time a few years ago with this sort of thing in mind and eventually dropped it.