This is not easy to implement.
Really? I don't know how it is implemented,
First it depends on the platform. And then it is typically from the video rendering thread.
But if you think it's easy, you're welcome to propose a patch.
Besides, I believe there is no way to determine whether an area of the video is "active" in some way, or not.
It is up to a user to determine what is active or not. I want to show popup menu for video area for right click and toggle full screen on left button double click. By the way, VLC player itself does it and DVD menu works there.
VLC does not filter events. It just dispatches them to both the DVD menu VM and the UI. It so happens that the UI handling was designed to not conflict with DVD menus: a single left click has no effects in the VLC UI.
If your application reacts on left mouse clicks, then DVD menus will not work anyhow.