This is mostly useful for SDR mode where previously we would output 203
nits, which on Windows is considered HDR, because reference white is
fixed at 80 nits in SDR mode. Which in turn causes additional
tone-mapping when using scRGB output.
Note that for SDR transfers this doesn't change the luminance, but
instead causes more aggressive tone-mapping, might not be fully
expected. But maybe we should follow system setting for better of for
worse.
Fixes: https://github.com/mpv-player/mpv/issues/17850
Not fully, because when ICC profile is embeded in content, libplacebo
will override our luminance, this will be fixed separately.
Kacper Michajłow
62f1494661