I'm glad to inform that you can easily set Filmage Screen for Mac as a default media player to play video files. To do that, please follow the following steps:
1. Open Finder, choose a video file and right click -> then choose Get Info; or click a file and tap command + i;
2. Click Open with -> Select Filmage Screen > Change all...；
3. In the popped window, tap Continue. Then Filmage Screen will be your default player.