Ok, strange.
You said " I've tried all combinations of 4K, and UHD each with 4:3, 16:9, 3:2, and yet the bars remain, always. Not sure I understand how aspect ratio affects the video, but I'm not an expert, so... "
The native video you shoot at 4096 x2160 isn't 16:9 but the 3840 x 2160 is...