Thumbnail Problem with h256/hevc videos (from iPhone)

[TomComm27]

Hello,

I am using a Qnap TS-253D (FW QTS 5.1.8.2823) with 8GB Ram. I want to use Jellyfin purely for my “management” of smartphone photos and videos.
Unfortunately Jellyfin does not create thumbnails no matter what I try.
It is about 1080p HEVC.

Thank you,
fg Thomas