Use X-WinFF (FFmpeg GUI) with -vf "transpose=x"
command to batch transpose videos.
On older FFmpeg builds the syntax for that command differs and needs to be adjusted
Possible parameters for x are:
0 = 90° CounterCLockwise and Vertical Flip (default) 1 = 90° Clockwise 2 = 90° CounterClockwise 3 = 90° Clockwise and Vertical Flip
The screenshot below shows where to enter the additional transpose command.
I've done a quick test and it works. You could also re-encode the video as you wished.
Maybe you want to "rotate" the aspect ratio too. Just add -aspect x:y
to the command-line
Example to rotate a 16:9 aspect ratio video
-vf "transpose=1" -aspect 9:16
Example to rotate a 4:3 aspect ratio video
-vf "transpose=1" -aspect 3:4