A VESA standard interface for synchronizing 3D glasses to a home theater projector via radio frequencies (RF). An emitter plugs into the 3D port and transmits signals that synchronize shutter glasses with the projected stereo frames. Typically mounted in the ceiling with no convenient line of sight to viewers' glasses, 3D home theater projectors cannot send infrared signals and must use radio frequencies. See
3D glasses and
front-projection TV.