Canon EOS RP Instruction Manual page 456

Recording HDR Movies
[ z : Movie cropping] is not available.
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Since multiple frames are merged to create an HDR movie, certain parts of
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the movie may look distorted. During handheld recording, camera shake may
make the distortion look more noticeable. Using a tripod is recommended.
Note that even if a tripod is used for recording, afterimages or noise may
become more noticeable when the HDR movie is played back frame-by-frame
or in slow-motion compared to normal playback.
Image color and brightness may change significantly for a moment if you
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change settings for HDR movie recording. Also, the movie will not be updated
for a moment, and the frame stops momentarily. Be aware of this when
recording movies to external devices via HDMI.
The recording size is L6X (NTSC) or L5X (PAL). Note that
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movies are recorded in HD when EF-S lenses are used.
ISO speed is set automatically when you record HDR movies.
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