Batch rotate videos. Note: This will stream copy the bitstreams, so no encoding is performed. Only the metadata of the first video stream (v:0) is changed here and the player will show the video in a rotated way. (Not all players will support this.)

.rotate-videos

# Works on the latest ffmpeg
# Source, Stackoverflow http://bit.ly/2k960G7

# brew install ffmpeg

# Default for iPhone
ext=m4v

# Set your directory
for f in /some/dir/*.$ext; do
    new=${f/%.$ext/-rotated.$ext};
    ffmpeg -i "$f" -c copy -metadata:s:v:0 rotate=270 "$new"
done