did you notice that:
gohai Gottfried Haider:
Not active here any longer (and won’t be notified if you mention me).
no idea if there will be help from anybody soon?
i could verify your problem:
all GStreamer related sketch not run on my RPI3B+
testing under RASPBIAN stretch AND buster
++ while camera and capture sketch works
++ also use the new VLC app on RPI to check if can play the video-file in question without problem.
i tried to play with that and failed ( but not fully )
so i do not recommend, but you might follow me here