Works:
Video with relative URL
[videoplayer=attachs/260402_8158i6_Flatterbane_LS58.mov width="600"]
260402_8158i6_Flatterbane_LS58.mov
Does not work:
Video with complete URL
[videoplayer=https://foss.weststadtaktivkasse.de/myfp/fp-content/attachs/260402_8158i6_Flatterbane_LS58.mov width="600"]
260402_8158i6_Flatterbane_LS58.mov
Given file does not exist.
Alternative: HTML-Embedding