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EagleTree use a technique based on the closed caption TV system for sending data over a video stream. It works very well and to the point where the video link is quite impaired. It is part of the OSD Pro system which sends data to the EagleEyes ground unit which then separates the data out for use with GoogleEarth and local storage etc.
EagleTree uses the vertical interval to encode the live GPS position and height data into the video stream. It is then decoded by the EagleEyes ground station and drives the pan tilt servos attached to the tracking antenna to follow the aircraft.