The new Epson W39 and W49 projectors include two HDMI Ports.
One port will be used with either the AppleTV or Chromecast.
The other will be connected to the HDMI port on the panel with the USB Camera port. It is a box on the wall near the teacher desk.
You can use the HDMI port here to plug in another video source, eg: a dvd/bluray player or a computer with HDMI output.