How do I prevent the auto-focus from bouncing on my Galaxy J7 smartphone?
Okay, I found the answer.
After I start recording, I can click for a second or so on the screen where I want the focus to be. The camera is going to make that item appear in focus and then block the focus to that point until I cancel it.
There should be an (AF) button appearing on the side. Clicking that button allows to go back to the auto-focus mode.
Note that there seems to be two modes: one when you do this when you're not recording and one when you are already recording. At this point I have not found the real difference, but the items (buttons) appearing on the screen are different. So I would imagine that there is some kind of a difference between both modes.