Canon EOS 5D Mark III Instruction Manual (en)

 Menu Function Settings
HDMI output + LCD
This is for recording the HDMI output image to an external recording 
device. [No mirroring] is set by default.
If you set [Mirroring], the movie displayed on the LCD monitor as it 
is being recorded can also be displayed from the HDMI output. Note 
that the video from the HDMI output will be displayed without the 
shooting information or masking for indicating image area (output 
without information overlay: through display).
If [No mirroring] is set, the movie will be displayed on the LCD 
monitor, but if there is HDMI output, the LCD monitor will turn off. 
With this setting, the movie from the HDMI output will show the 
shooting information and masking for indicating image area. 
However, by pressing the <
B> button, you can eliminate the 
information from the output.
If the HDMI movie is output without information, the card’s remaining 
capacity, battery level, internal temperature increase (p.247) and other 
indicators will not appear on the HDMI output screen. Be aware of this if 
[No mirroring] is set. If [Mirroring] is set, you can check these 
indicators on the LCD monitor.
When you are not shooting movies, the power will turn off automatically 
in accordance with the auto power off time. If you are recording the HDMI 
output image to an external recording device, setting [52: Auto power 
] to [Disable] (p.55) is recommended.
Audio is not output during HDMI output.
Even if [Mirroring] is set, no image will be displayed through the HDMI 
output when a movie is played back or menu is displayed.
When you stop movie shooting, the HDMI output image will pause (frame 
stop) while the movie is being recorded to the card. After the recording is 
completed, the image will be displayed normally.
Simultaneous output from both HDMI and A/V OUT is not possible. The 
movie will be output to the cable that was connected to the terminal last. 
During A/V OUT output, nothing will be displayed on the LCD monitor.
The brightness of a movie shot by the camera and that of a recorded 
HDMI output image on the external recording device may differ 
depending on the viewing environment.