[FFmpeg] Horizontal Flip Video, symmetrical display playback

The first step: the width of the output video is set to twice times the width of the source video (w: Specifies the width of the output image; IW: Enter the width of the video):

Ffmpeg-i INPUT.MKV-VF Pad=w=2*iw output.mkv

Second step: SOURCE Video Horizontal Flip:

Ffmpeg-i INPUT.MKV-VF Hflip hflip.mkv

Step three: Overlay the horizontal flipped video hflip.mkv on the output.mkv (x: Set overlay input overlay on main input, and w:overlay input width):

Ffmpeg-i output.mkv-i Hflip.mkv-filter_complex overlay=x=w symmetry.mkv

You can combine these three steps into one step:

Ffmpeg-i Input.mkv-filter_complex "[0:v]pad=w=2*iw[main]; [0:v]hflip[overlay]; [Main] [Overlay]overlay=x=w "symmetry.mkv