1ffmpeg -i input.mkv -c:a copy -s hd720 output.mkv
2This modifies the video to 1280x720 in the output, but you can set the width and height manually if you want:
3
4ffmpeg -i input.mkv -c:a copy -s 1280x720 output.mkv
5This produces the exact same output as the earlier command. If you want to set custom sizes in FFmpeg, please remember that the width parameter (1280) comes before height (720).