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First ever HDR video on Sway + mpv. The left screen is SDR, right one is HDR. Of course it's impossible to tell the difference on the picture because my camera is SDR. You'll have to take my word for it: the right screen shows a lot more various colors (orange, yellow, white) while the left one is mostly uniform yellow-white.
This is the super basic hacked together version which just forwards HDR metadata received from mpv and forces a modeset, still needs tons of work.