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
$ ffmpeg -r 1 -i frame%d.png -pix_fmt yuv420p video.mp4
and obtain a black 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.