Best way to batch rotate 3000+ h.264 videos? I have approximately 3000 short video clips, each about 3 seconds in duration. I need to rotate each of them 90 degrees. What is the best way to do this? I have Adobe Creative Cloud subscription, as well as access to both Windows and Mac machines. Looking for the easiest solution to automate/batch process the rotation of so many videos.

If you were wondering - the videos are part of an e-learning course on lumber. The learner views each randomly selected video, which is just a short clip of a piece of lumber rotating. The videos were shot so that the lumber (2x4s, etc.) were horizontal. But now the client wants the lumber to be vertical in the clips.
Use ffmpeg and the "transpose" filter as "poor" suggested. For example, if your files are mp4 and are in the current directory:

mkdir -p rotated
for f in *.mp4; do ffmpeg -i "$f" -vf transpose=2 -c:a copy -metadata:s:v rotate="" rotated/"$f"; done



The transpose value can be "1" or "clock" for clockwise rotation, "2" or "cclock" for counter-clockwise rotation. There are other values which will also apply a flip.
The audio will be stream copied to avoid unnecessary re-encoding.
The video stream rotation metadata is cleared in this example. Otherwise ffmpeg will copy it from the input to the output resulting in an incorrect rotation for players that pay attention to this metadata (some do, and some don't).


Another example, more verbose and flexible, and which keeps the rotated file in the same directory with a new name:

ext=mp4
for f in /some/dir/*.$ext; do
    new=${f/%.$ext/-rotated.$ext};
    ffmpeg -i "$f" -vf transpose=2 -c:a copy -metadata:s:v rotate="" "$new"
done