One of my video is upside down. It turns out that the AutoRotation metadata is set wrong to Down whereas it should be Up according to my other videos:
$ exiftool -s input.mp4 | grep AutoRotation
AutoRotation : Down
I tried using exiftool from the command line to change the tag:
$ exiftool -AutoRotation=Up input.mp4
Warning: Sorry, AutoRotation is not writable
Nothing to do.
How can I change (or remove) a specific mp4 tag on linux?
The AutoRotation tag is a GoPro specific tag and is unlikely to be editable unless GoPro has a program that edits the metadata it embeds.
Using exiftool, a better option would be to edit the Rotation tag (e.g. -Rotation=90/180/270), which is actually not a single tag but a case of exiftool manipulating multiple tags in order to achieve the rotation desired (see the entry on the Composite tag page).