These still images were captured when browsing the full 5K7 videos with VLC Media Player on my PC. The videos were exported in fisheye view to MP4 files using the Windows Insta360 Studio for ONE X (Beta).
I didn't use VLC's screen capture as it would copy the full 5760 x 2880 pixels frames. Instead I panned around and framed what was on my HD screen. I used Alt + PrtScrn to capture it to the clipboard for editing.