sceneMaxNits

The brightest level of this frame's scene in nits, from dynamic HDR metadata that travels with the frame, such as Dolby Vision's level 1, or null when the frame carries none.

hdr describes the whole title, so a tone mapper that knows only it compresses every scene for the title's brightest highlight. A dark scene then loses brightness it never needed to give up. toneMapPeakNits is the peak a tone mapper rolls off from, with this taken first.