Comment by PunchyHamster

> A word processor can save it's state at an arbitrary point...

As ENTIRE STATE. Video codecs operate on essentially full frame + stream of differences. You might say it's similar to git and you'd be incorrect again, because while with git you can take current state and "go back" using diffs, that is not the case for video, it alwasy go forward from the keyframe and resets on next frame.

It's fundamentally order of magnitude more complex problem to handle