Movie thumbnail showing "play triangle"

Hi! I am running an instance of nextcloud on a sbc, with ten users (friends and family). Very very grateful towards the people who created nextcloud and help us to claim ownership of our data. I just discovered the feature to enable previews for movies =) ! Great, I had overlooked this for >2 years… (manual here:

But: Now movies can not be discerned from pictures (e.g. if the filename does not begin with “VID…”). Any way to alter the preview generation code to add a “play triangle”, “lateral film strips” or something similar clearly marking the thumbnail as belonging to a video/movie file?

This sounds promising, although I’m not fit enough to alter the preview generation code: