overlaycomposition: proposal to improve handling of overlay for external window whose dimensions do not match video dimensions
There are (at least) two types of overlays - those tied to the video frame coordinate system, such as object detection bounding boxes, and those tied to the sink window coordinate system, such as text. User may want to render text at an arbitrary position in the window, and bounding box at an arbitrary position in the video frame. It would be nice to clip the boxes to the video frame. The sink itself knows about the video frame coordinates relative to the window.
Also, we don't want to scale the overlay rectangle, as text quality degrades.
I propose that the overlay rectangles be rendered as either relative to the window coordinates, or relative to the video frame coordinates, using a flag.
Rectangles should not be scaled when rendered - they will be pixel-to-pixel match of the window region. Or, if we want them scaled, scaling factors can be provided.