[serf]

i've used AutoHotkey for this in the past.

Here's a relevant forum link.[0]

I think ahk is mac compatible, but I haven't tried it.

I had a similar problem in college, to which I made a bash script that called cow-say over and over again to make the cow look as if it were typing, and then recorded that section of the screen.

Clunky but effective.

Good luck.

[0]: https://www.autohotkey.com/boards/viewtopic.php?t=26761

[2rsf]

autohotkey is good for the purpose, the only question is whether you can make the app (or cmd line window) invisible