LG G3 - Manual (Page 121)

Camera and Video 112
Note: Do not press too hard; the touch screen is sensitive enough to pick up a light, but firm touch.
Dual Play
Dual Play (connected wired or wirelessly two displays) can be run on a different screen.
Note: Connect two devices using a wired (Slimport-HDMI) cable or wirelessly (Miracast).
The connectable device can be a TV or a monitor supported by a HDMI cable or Miracast.
The Gallery and Video apps are supported on Dual Play.
Tap once when two displays are a different status (i.e. the monitor is playing a video and your
phone's video app is displaying an empty screen), then Dual Play will start.
Not all videos are supported by Dual Play.
Dual Play operates at 1280X720 or higher display resolution.