Canon EOS 70DN Basic Instruction Manual page 589

The manually set ISO speed changes when switching to movie shooting.
If you shoot a movie when [Maximum: H (25600)] is set with [ISO
speed range] and ISO speed is set to "H" (25600), the ISO speed will
switch to "H" (12800) (during movie shooting with manual exposure).
Even if you switch back to still photo shooting, the ISO speed will not
revert to the original setting.
The exposure changes during movie shooting.
If you change the shutter speed or aperture during movie shooting, the
changes in the exposure may be recorded.
Zooming the lens during movie shooting can cause changes in the
exposure regardless of whether the lens' maximum aperture changes
or not. The changes in the exposure may be recorded as a result.
The subject looks distorted during movie shooting.
If you move the camera to the left or right quickly (high-speed panning)
or shoot a moving subject, the image may look distorted.
The image flickers or horizontal stripes appear during movie shooting.
Flickering, horizontal stripes (noise), or irregular exposures can be
caused by fluorescent light, LED bulbs, or other light sources during
movie shooting. Also, changes in the exposure (brightness) or color
tone may be recorded. In the <a> mode, a slow shutter speed may
solve the problem.
When I shoot still photos during movie shooting,
the movie shooting stops.
Setting a lower image quality for still photos and shooting fewer
continuous still photos may resolve the problem.
Time code is off.
Shooting still photos during movie shooting will cause a discrepancy
between the actual time and time code. When you want to edit a movie using
time code, it is recommended not to shoot still photos during movie shooting.
Troubleshooting Guide
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