Canon EOS-1D X Mark III Advanced User's Manual page 735

2.
Set the recording method.
/ separate
Select [Enable] for automatic configuration of the recording method for
still photos and movies. Still photos are recorded to card
movies to card
or not inserted. Movie recording is not possible if card
inserted.
Caution
Specifying [Enable] will make [
options], [
unavailable.
. Still photo shooting is not possible if card
Record/play], and [
735
is full or not
Rec options], [
Record/play]
and
is full
Rec