So, as it turns out…
You have to use the stuff on the post page, not use the built in wp stuff for it to work.
This is a post with video (my montage)
So the video wasn’t inserted in the slider, but maybe the image will
The video wasn’t inserted in the post – it was just a link, well, not even a link – just text.
Another Test post for the featured slider
This one, without images, could appear as text if there was a working version of the slider!