Incidentally, when accessing https://legacy.mapillary.com/map/upload/vi you’ll see a new green button : “Choose video file” ; text above reads ;
" Upload Video
Upload a video and an accompanying .gpx file to process it into a sequence of geolocated images.
Note: This legacy uploader is no longer actively maintained. We recommend using our Desktop Uploader instead. Advanced users can also use the Mapillary python tools. "
Sounds like the legacy tool was repurposed to take videos and accompanying .gpx-files?
There’s no mention of which video format(s) can be accepted - may be a case of anything goes initialy?
My usual tuppence, k.