ffmpeg

INCOMPLETE AF

Convert video to audio

ffmpeg -i video.mp4 audio.mp3 # add -c:a & friends if needed

ffmpeg -i video.mp4 -c:v h264_qsv output.mp4

ffmpeg -i video.mp4 -ss 00:00:00 -to 00:00:30 cut.mp4

ffmpeg -i video.mp4 -vf "scale=640:360" out.mp4

If you want to preserve aspect ratio:

ffmpeg -i video.mp4 -vf "scale=640:-1" out.mp4

Horizontally:

ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex hstack out.mp4

Vertically:

ffmpeg -i video1.mp4 -i video2.mp4 -filter_complex vstack out.mp4