Canon EOS-1D X Mark III DSLR Camera (Body Only) - Manual (Page 273)

Caution
The card's writing/reading speeds required for recording movies (card
performance requirements) vary depending on the movie recording quality.
Before recording movies, see
Cards That Can Record Movies to check card
performance requirements.
Movie Recording Size
Image size
Image Size Aspect Ratio
5472Ч2886 17:9
4096Ч2160 17:9
* 4096Ч2160 17:9
3840Ч2160 16:9
1920Ч1080 16:9
* Movies can be cropped around the center of the image, as if recorded with a telephoto lens.
Caution
If you change the [ : Video system ] setting, also set [ : Movie rec quality ]
again.
Other devices may not play movies such as 4K,
/ , and High Frame
Rate movies normally, because playback is processing-intensive.
Apparent resolution and noise vary slightly depending on movie recording quality
and settings for the lens used.
Note
To obtain better performance with the card, formatting the card with the camera
before recording movies is recommended (
).
Movies cannot be recorded in HD or VGA quality.
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