Canon EOS 5D MARK IV Instruction Manual page 571

Playback Problems
Part of the image blinks in black.
[33: Highlight alert] is set to [Enable] (p.401).
A red box is displayed on the image.
[33: AF point disp.] is set to [Enable] (p.402).
During image playback, the AF points are not displayed.
When you play back an image applied with distortion correction
(p.209), the AF points are not displayed.
The image cannot be erased.
If the image is protected, it cannot be erased (p.412).
The movie cannot be copied.
Copying movie files exceeding 4 GB may not work. For details,
see page 435.
Still photos and movies cannot be played back.
The camera may not be able to play back images taken with
another camera.
Movies edited with a computer cannot be played back with the
camera.
Operation sound and mechnical sound
can be heard during movie playback.
If you operate the camera's dials or lens during movie shooting,
the operation sound will also be recorded. Using the Directional
Stereo Microphone DM-E1 (sold separately) is recommended
(p.363).
Troubleshooting Guide
569