Black borders in thumbnails

[Kagami]

Hi,

Thanks for great plugin, I like it a lot. Mostly works without issues.
But one visual unfortunate glitch is that it generates black borders for small video thumbnails in icon view in Finder. This doesn't happen with photo thumbnails. See attached screenshots.

I found this issue #19 which was resolved.
But then it was discussed again here #63 (comment) and it seems to be a flaw of Quick Look Plugin API? So no workaround possible? Please confirm if so.

Although cover thumbnails for mkv look fine. See last screenshot. Is it possible to generate thumbnails from video frames in the same way?

Thanks.

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[Marginal]

Finder decorates thumbnails according to file type - thin white borders for pictures (like a printed photo), black borders for movies (like letterbox mattes), no borders for movie cover art (like a physical film poster?). There are also some other obscure/historical decorations.

I could suppress the black borders or replace them with something else, but I wanted to stay consistent with macOS behaviour.