See again in http://nplayer.tv/blog/how-to-connect-nplayer-with-a-smart-tv/
First, play a video on nPlayer and tap the Tap the icon in the picture. (See the picture)
1-1) Please ensure the smart TV and nPlayer are connected on the same network.
When you tap on the menu, you may see the name of smart TV on.
2-1) Tap the name, the smart TV will automatically play the video.