A clean HDMI output is an HDMI video that doesn’t have burn-in data taking over your screen. In simple words, the output is “clean”, without the UI elements appearing on your screen.
Which cameras have clean HDMI out?
EOS R, EOS 5D Mark IV, EOS-1D X Mark III These cameras have a menu to allow clean HDMI outputs. Resolution depends on the selected movie resolution. The default is that menus and displays are shown on the external display, so you need to select the external display only as in the screen above.
What can I use to clean my HDMI port?
Isopropyl Alcohol and Cotton Buds Then gently and carefully rub it on the dirt on your HDMI port. You don’t need huge amounts of alcohol on the cotton bud for this to work. Once you’ve done this, leave it to dry out before plugging in any cables, or switching on your device.