Canon EOS REBEL T8i Advanced User's Manual page 719

Expanded ISO speeds cannot be selected for movie recording.
Check the [ISO speed] setting under [
Expanded ISO speeds are not available when [
[Enable].
The exposure changes during movie recording.
If you change the shutter speed or aperture value during movie recording, the changes
in the exposure may be recorded.
Recording a few test movies is recommended if you intend to perform zooming during
movie recording. Zooming as you record movies may cause exposure changes or lens
sounds to be recorded, an uneven audio level, or loss of focus.
The image flickers or horizontal stripes appear during movie recording.
Flickering, horizontal stripes (noise), or irregular exposures can be caused by
fluorescent lighting, LED lighting, or other light sources during movie recording. Also,
changes in the exposure (brightness) or color tone may be recorded. In <
using a slower shutter speed may reduce the problem. The problem may be more
noticeable in time-lapse movie recording.
The subject looks distorted during movie recording.
If you move the camera to the left or right (panning) or shoot a moving subject, the
image may look distorted.
I cannot take still photos during movie recording.
Still photos cannot be taken during movie recording. To take still photos, stop the movie
recording and perform viewfinder shooting or Live View shooting.
: ISO speed settings].
: Highlight tone priority] is set to
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