Nikon Z8 User Manual page 594

Extended Oversampling
G button U 1 video recording menu
Selecting [ON] optimizes image readout for improved image quality.
Extended oversampling applies when [3840×2160; 60p] or [3840×2160; 50p] is selected for
[Frame size/frame rate] and [FX] is selected for [Image area] > [Choose image area] in the video
recording menu.
Note that the drain on the battery increases when [ON] is selected.
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Extended Oversampling