Nikon Z 9 Reference Manual page 309

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[ProRes 422 HQ 10-bit (MOV)] footage is output at a YCbCr value of
4:2:2 and a bit depth of 10 bits, regardless of the option selected for
[Frame size/frame rate].
•
[H.264 8-bit (MP4)] footage is output at a YCbCr value of 4:2:2 and a
bit depth of 8 bits, regardless of the option selected for [Frame size/
frame rate].
D
Recording to External Recorders That Support a Bit Depth of
10 Bits
The HDMI signal will be output at a bit depth of 10 bits only to HDMI
recorders that support this option.
Recorders
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