When I generate a video starting from a sequence of PNG snapshots, the output video is black.
Here is a minimal working example: I generate the video from these two frames with the following command on Ubuntu 16.04.4 LTS and produces a black video MP4 file.
ffmpeg -r 1 -i frame%d.png -pix_fmt yuv420p video.mp4
Do you know a way around this?
I know that a similar question has been asked, for example, here, but the solution does not solve the problem in my case.