After merging mp4 files, the resulting video plays only audio (black screen)

[WilderMinds]

After merging two different videos (videoA.mp4 & videoB.mp4), for some reason, the resulting video (output.mp4) just plays audio with the accompanying black screen

What's odd is that when I merge (videoA.mp4 & videoA.mp4) or (videoB.mp4 & videoB.mp4), the resulting video is fine (video is visible, audio is audible)

Both videos are 1080*1920 and 30fps

Help please

[Deleted user]

@WilderMinds this could be due to the difference in codec of the videos you are trying to merge.
That is there might be a difference in framerates of videos one might be fast or slow from the other video.
or different orientation, videos might be taken from the front or rear camera individually.
see also #118