I implemented it but in my Mediathek there is a uncredible high number of automaticly generated preview pictures. I did not upload own. They are generated from YouTube and I can’t delete theme in the mediathek. What can I do?
Hi @user14136, my apologies for the delay 
Since you’ve mentioned that you’re using WordPress Mediathek, the issue might be rooted in that tool, as it’s not connected to our widgets 
But I believe the WordPress Mediathek support team should help you resolve this issue