For those of you that always used to display a video window on a computer display, you must be quite familiar with this phrase, “Video Overlay”.

Generally, video overlay is the device that being used to connect between the graphics card analog VGA output and the monitor’s input, where it can form a connection named “VGA passthrough”. To be more precisely, the device can modify the VGA signal and insert the analog video signal overlay into the picture. As a result, the screen will be filled by the signal that comes from the graphics card.

Normally, the driver software will inform the video overlay device about the desired position of the video window on screen. However, since this method requires greater processing power of modern graphics cards, thus it’s hardly been used in nowadays!

The main objective of this project is to add telemetry information to a video signal from a camera mounted on an RC-airplane. This concept is based on an OSD project called AVROSD. By using this AVROSD, you can develop several OSD implementations.

For your information, some of the video overlay devices can write the digital video signal directly into the graphics card’s video memory as well!