DJI iOSD is specially designed for DJI autopilot system duringthe FPV flight or other aero-modeling activates. DJI iOSDcan transmit video and iOSD information in real time, which will help you to obtain the aircraft status information during a FPV flight. It can display power voltage, flight velocity, height, distance from the home point, horizontal attitude, GPS satellite number, etc. iOSD and video information are superposed on the receiver, making iOSD data clearly visible and bringing you a more involved flight experience.

For more information:
http://www.dji-innovations.com/products/iosd/overview/