XnView Software

Welp, that solved the problem. Apparently the box wasn't ticked by default though? I'm sure I had never seen the "Custom filters" screen before, so I didn't do that.

Yes. And if I open them from xnview mp, they open with its video player. But the thumbnails are still just vlc icons.

Yes, all and any formats. I don't get thumbnails for any videos. Are you mentioning that it's based on ffmpeg because of ffmpeg's thumbnailer? Do you suspect it's not being used?

XnView: MP 0.91 Beta 3 64 bit (I tried the stable version as well)
OS: Windows 10 64 bit
Effect: Video thumbnails are not displayed
I read that the app is supposed to show thumbnails for video files, but for me it's not doing that. All I see is VLC's traffic cone icon. This happens with all video ...