Originally Posted by MatrixPC
usedualmon=true was developed for the pupose of having video play fullscreen on 2ndary monitors ultilized graphic card video overlay function. While video play on the back, you can have GPS showing on main monitor.

If setting usedualmon=false, you can not having video play on 2ndary monitor and gps on at the same time because it will force video to stop and play music.

It also usefull for those who has music video playing and having gps showing instead of the video which is illegal is most/all places while vehicle is in motion.