Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 255)

2.
Set the recording mode to < >.
Press the < > button, then turn the < > or < > dial for
selection.
3.
Focus on the subject.
Before recording a movie, focus with AF ( ) or manual focus ( ).
By default, [ : Movie Servo AF ] is set to [ Enable ] so that the
camera always keeps focusing ( ).
When you press the shutter button halfway, the camera will focus with
the current AF method.
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