AF in Camera - Please inform me

I have Samsung A7 2017 and when I start recording video... there is an "AF" button on lower left corner.
I understand it is Autofocus, but like to know :-

If the AF button is there - Does It mean while recording camera is actively auto-focusing on every object I move my camera to ?

What if AF button is not present and missing - Does it mean camera is in manual mode ?

PS: Basically confused when its off/on.

Plz Explain me

from Android Authority Forums http://ift.tt/2qtCEro
via IFTTT