You can easily do that with ffmpeg (https://ffmpeg.org/). This command will convert every mkv file in your current folder to a clip folder, ready for upload. (DMs open)
for %i in (*18-18-51.mkv) do ffmpeg -i "%i" -ss 00:00:00 -t 00:01:00 -vf "crop='in_h*9/16:in_h'" "clip/%~ni_clip.mp4"
Comments
for %i in (*18-18-51.mkv) do ffmpeg -i "%i" -ss 00:00:00 -t 00:01:00 -vf "crop='in_h*9/16:in_h'" "clip/%~ni_clip.mp4"