Canon EOS-1D X Mark III Advanced User's Manual page 274

4K Movie Recording
Recording 4K movies requires a stable card with a fast writing speed. For details, see
Cards That Can Record
4K or High Frame Rate movie recording greatly increases the processing load, which
may increase the internal camera temperature faster or higher than for regular movies. If
a red icon appears during movie recording, the card may be hot, so stop
recording the movie and let the camera cool down before removing the card. (Do
not remove the card immediately.)
From a 4K movie, you can select any frame to save to the card as a JPEG still image
( ).
Caution
AF is not used to focus when
points are displayed. Also note that the focus guide is not displayed, even with the
lens's focus mode switch set to <
Movies.
/
>.
274
or / is set. No AF