minimOSD is a board that can read the flight data (MAVlink data) from Ardupilot and 

combine flight information symbol and input video signal into composited video signal. You can connect the video signal PAL/NTSC to your video transmitter. Here is my minimOSD test on my multicopter.

1. display setting using OSD config:

2. Video output result from minimOSD:

Summary:

The minimOSD is quite useful on FPV, but it is a bit expensive on its price.