Insert a black frame between each frame and double the output FPS

So I am looking for a way to add a black frame in between each frame of a current video. What I am trying to do it add a blanking phase to a video to give it a film look. So the pipeline is a 59.94 fps video and add a black frame in between each of the source video frames and create an output video that is 120fps with a real frame, black frame, real frame, black frame, etc. Is there an easy way of doing this?

1 Answer

If

1. your video is constant frame-rate, and
2. you know the framerate,

you can run

ffmpeg -i in -vf fps=120000/1001,drawbox=t=fill:c=black:enable='mod(n\,2)' -c:a copy out

where 120000/1001 is supposed to be double the input fps.