Without any custom plug-ins, you can read files and also communicate via web protocols. The file access would be the easiest thing, but only for stored data. Wouldn't really be useful for real-time. If you need real-time updates, you can setup a simple HTTP server (like in Python) and send UDP packets to Godot. Otherwise, if the video capture program is your own, you can write a GDNative plug-in to communicate directly with (or just integrate into) Godot via C++.