Sony RX100 M4 – set focus before video?

[guyburns]

QUES
Can a user set focus on the RX100 M4 before videoing?

I'm tossing up between the Sony RX100 M4 and the Panasonic LX100. The former may be easy to discard if what Dpreview.com says is correct:

"AF-S mode isn't available in video mode, so you can't use it to set focus before recording"

Here's an example of where I may want to set focus first, and keep that focus: I want to capture in extreme slow-motion, slides falling through the air. I set the camera up horizontally, focus on a sheet of paper held in the air in the right position, remove the paper, start the camera, then have an offsider who is standing on a chair, tip out a bucket of slides.

Sony's 960 fps is just what I need, but I have to be able to set focus first. I don't want the camera hunting to find focus because the action will be over in tenths of a second.

[armand]

Couldn't you use manual focus for something like that?

[guyburns]

Manual focus – yes. I didn't think of that. But if the camera does not allow AF-S, maybe it would also override manual focus when video is turned on, and switch to AF-C.

Anyone with a RX100 IV know whether you can set focus before videoing, and have that focus retained?