Cleaning up some backup files to get rid of an old drive after a crash a year ago, I found a remaining .webm lying around. Sourced off a defunct youtube video. Using ffmpeg -c copy -f framemd5 I find one frame that differs. Video. VP9.
Not that I can see any difference. But I don't find an error either: "0 decode errors". Which makes me curious: How to get a most zealous scanning?