show tracked object in Video using OpenGL

Dear All,

I need help for OpenGL. I am extending an existing OpenGL project with new functionality.
I can play a video stream using OpenGL with FFMPEG. Some objects are moving in the video stream. Co-ordinates of those objects are know to me.

I need to show tracking of motion for that object, like continuously drawing a point or rectangle around the object as it moves on the screen.

Any idea how to start with it?