You can solve this problem either in Elmedia Player or in the system preferences on your Mac.
Go to Elmedia Player Preferences > Interface. Find the Disable screen saver option and select Always.
Go to System Preferences > Energy Saver. Make sure that the following option(s) are checked: “Prevent computer from sleeping automatically when the display is off” and “Wake for Wi-Fi network access“. The option “Put hard disks to sleep when possible” should be off.