Is it possible to submit a run with only demos and not recorded footage with software such as OBS?

As it says in the rules "Runs cannot be submitted with only demo proof if the game is paused mid-run. Runs that would end up in the top 10 have to be submitted with a live video and demo proof."
So if your run isn't in the top 10 and you don't pause your game, you can submit just the demos