ffmpeg -i input.mkv -vf scale=-1:720 -c:v libx264 -crf 18 output.mkv
Downscaling requires re-encoding the video, so it will take some time depending on your computer's CPU or GPU speed. saw vi 1080p mkv to 720p free
The standard theatrical rate is 23.976 fps. For the smoothest playback, ensure HandBrake is set to "Same as Source" for the framerate. ffmpeg -i input