Behind the scenes, look for when they are "marking," which is leaving little piece of tape or otherwise on the ground where the actors are standing. The focus puller will make indications on their focus ring to match these; as long as the actor "hits their mark" the focus will be dead on. A majority of time the operation is fully manual (though possibly remote to the camera)
That's how I remembered it too. And that's also then one of the major differences between this app and an actual professional camera - because on a smartphone you only have autofocus. Which works most of the time, but I've had some recordings of concerts with weird lighting, smoke and other stuff which were out of focus for quite a few seconds. One of the most stupid things is when you try to take a picture of a bird or airplane in flight and your smartphone can't focus on it because it's too small. Why can't it just default to focus to infinity if it can't find anything to focus on?
