FFMPEG

Scale video to 720p

This also makes sure the width is a multiple of 2 (4), so ffmpeg doesn’t freak out and just copies the audio.

ffmpeg -i input.mkv -filter:v scale="trunc(oha/2)2:720" -c:a copy output.mkv

If you need to scale to any other resolution, like 576p, 1280p, etc, just replace “720” with the appropriate number.