Canon EOS R6 Mark II Mirrorless Camera with 24-105mm f/4-7.1 Lens - Manual (Page 359)

Aperture-Priority AE
[ ] recording mode enables you to set your preferred aperture value for movies. ISO
speed and shutter speed are set automatically to suit the brightness and obtain standard
exposure.
1.
Set the recording mode to [ ].
Turn the Mode dial to < Av >.
2.
Set the aperture value (1).
Set it by looking at the screen as you turn the < > dial.
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