Hi @vahe4060, welcome to the forum 
QGroundControl does have a developer guide that may be handy, and a good place to start in the codebase would presumably be the VideoManager.
There may be some other community members who could help (e.g. this forum thread could be relevant), but on the Blue Robotics side we don’t provide support for custom QGC development, since it’s not our application and most of our GCS development efforts are now focused on Cockpit.
The QGC developer docs do provide a link to a relevant forum where development questions can be more meaningfully discussed