Canon EOS Rebel T4i 18-135mm IS STM Lens Kit Instruction Manual page 179

When you press the shutter button halfway to autofocus during movie
shooting, the following phenomena may occur.
• Focus may become far off momentarily.
• The brightness of the recorded movie may be different from that of the
actual scene.
• The recorded movie may be momentarily still.
• The movie may record the lens operation noise. Lens operation noise may
be recorded.
• You may not take a still photo when focus is not achieved in cases such as
the subject is moving.
k Shooting Movies
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