If you just want to change the metadata such that mediaplayers that consider the flag play the file rotated, try something like:
ffmpeg -i input.mp4 -c copy -metadata:s:v:0 rotate=90 output.mp4
as found elsewhere on stackoverflow.
If you just want to change the metadata such that mediaplayers that consider the flag play the file rotated, try something like:
ffmpeg -i input.mp4 -c copy -metadata:s:v:0 rotate=90 output.mp4
as found elsewhere on stackoverflow.