Canon EOS-1 D X Mark II Instruction Manual page 375

Frame grabbing is not possible with Full HD movies or 4K movies shot
with a different camera.
Frame grabbing is not possible if the camera is connected to a computer.
Save the frame.
6
Select [OK] to save the frame
displayed on the screen as a still
photo (JPEG image).
Check the destination folder and
image file number.
Select the image to be displayed.
7
Select [View original movie] or
[View extracted still image].
The selected image will be displayed.
Grabbing a Frame from 4K Movies
375