The problem was I had renamed the files at the same time as updating Insta360 studio. The camera produces a pair of files, one for each lens, and has a naming convention that lets Insta360 studio pair and stitch them. The naming convention is underscore delimited, and requires the same pattern of underscores as the camera-generated file name. Also, the files ...
848 x 480 isn't an exact translation of 840x840 to a 16x9 stretch.
To think about aspect ratio, you need to consider what shape your image is now, and what shape you want it to be. If you have a 480x480 image that looks correctly proportioned on your computer screen, then it is using square pixels (ie each pixel is the same height as it is wide).
In fact, there are mostly 3 software for finding duplicate videos.
Video Compare https://www.video-comparer.com
Duplicate Video Search https://duplicatevideosearch.com
Duplicate Media Finder (my favorite) https://duplicate-media-finder.kdo-rg.com
All of them use fingerprints.