Canon EOS 5D Instruction Manual page 142

Movie Shooting Cautions
Camera's Internal Temperature Increase
If the camera's internal temperature becomes high, the <E> icon may
appear on the screen. When not shooting, turn off the camera.
If you take still photos while the <E> icon is displayed on the screen, the
image quality may be degraded. The image quality of movies is not
affected.
If the <E> icon is displayed and you keep shooting movies until the
camera's internal temperature rises further, the movie shooting will be
terminated automatically. Movie shooting will be disabled until the
camera's internal temperature decreases.
Playback and TV Connection
If the brightness changes greatly during movie shooting, that part might
look momentarily still when you playback the movie.
If you connect the camera to a TV set (p.157-158) and shoot a movie,
the TV will not output any sound during the shooting. However, the
sound will be properly recorded.
If you connect the camera to a TV set with an HDMI cable (p.158) and
shoot a movie in [1920x1080], the movie being shot will be displayed at
a small size on the TV. However, the actual movie will be properly
recorded at the movie recording size that was set.
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