Yes, you can!
Most older DVD Players or cable boxes have an S-Video or Composite output. You can connect via S Video or Composite cable from the DVD player or cable box to the projector. It is recommended to connect via scart (RGB) connection via adapter, if this is available.
Newer projectors have digital only ports; which is compatible with most current cable boxes and Blu Ray players and Media payers. Most game consoles will have an HDMI port available to use. The digital port is the HDMI port, which most newer Optoma projectors typically will have at least one or two HDMI ports for you to plug your sources into via a standard HDMI cable.
Please note that if you are trying to support 4K/UHD resolution if your projector supports 4K/UHD; it is industry common knowledge that you should use 15 feet or less HDMI cable to support that signal reliably.
If you know ahead of time prior to installation that your source(s) will be far away from your projector; then you could look into using a video extender if within your budget, like an HDBaseT extender or fiber optic HDMI. It is always best to consult your local AV Dealer for more integration tips and advice for your specific projector room environment for optimal results (Optoma Dealer Locator Tool)