You can use the following FFmpeg command to downscale a video by a factor of 2:
ffmpeg -i input.mp4 -vf "scale=iw/2:ih/2" -c:a copy output.mp4
Explanation:
-i input.mp4: Specifies the input video file.
-vf "scale=iw/2:ih/2": The video filter (-vf) applies the scale filter, which downsizes the width (iw) and height (ih) of the video by half (a factor of 2).
-c:a copy: This copies the audio stream without re-encoding.
output.mp4: The output video file.
This will create a new video that is half the resolution of the original one.