How to use MELT or FFMPEG for layering of a video (i.e. shifting an overlay of the same video by one frame to remove flicerking from LEDs)?
You would carry that out, like this:

ffmpeg -i in.mp4 -filter_complex \
  "[0]split=2[base][shifted]; \
   [shifted]setpts=PTS+1/TB/FRAME_RATE,format=yuva444p,colorchannelmixer=aa=0.50[shifted]; \
   [base][shifted]overlay"   out.mp4


setpts=PTS+1/TB/FRAME_RATE delays the overlay by 1 frame. Change the 1 to adjust delay.

format=yuva444p makes sure there's an alpha channel.

colorchannelmixer=aa=0.50 sets the alpha to 50%.

I haven't specified any encoding parameters, so the defaults will be used.