Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 271)

Note
Notes for movie recording
Each time you record a movie, a new movie file is created on the card.
Field of view (coverage) is approx. 100%.
Focusing is also possible by pressing the <
> button.
To enable starting/stopping movie recording by pressing the shutter button
completely, set [
Fully-press ] for [ : Shutter btn function for movies ] to [ Start/
stop mov rec ] ( ).
Monaural sound is recorded with the built-in microphone for movie recording ( ).
Stereo sound can be recorded by connecting an external microphone such as
Directional Stereo Microphone DM-E1 (sold separately) to the camera's external
microphone IN terminal, which will be used instead of the built-in microphone (
).
Most external microphones equipped with a 3.5 mm mini-jack can be used.
Focus preset during movie recording is available when using (super) telephoto
lenses equipped with this function released in and after the second half of 2011.
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