I agree completely. When there's a looping video below the fold, I'd rather start it with a click, instead of having to watch it up to twice just to see the clip from beginning to end.
But you won't. Because the clips are 5 to 20 seconds long. So its faster to just wait for the loop than even to move your hand to the mouse.
How are you scrolling? When I’m browsing and reading my hand lives on the mouse. On mobile it’s even easier to click to play. In either case, clicking on a video takes less than 1 second.
I do agree that extremely short loops can be a different story, but 20 seconds is by far over that time for me. 5 seconds is around the threshold.
I’m sure this preference varies by person.
My hand lives either on the space bar, or the page-down button. Both of which are far more efficient at scrolling through pages of text.
Neither pgDown nor space bar scroll.