video wall behind an object that is tracked with AR

Hi,
I am new to AR applicatons with Unity and I would like to ask you a question.
I need to creat an AR application which track some objects (i.e. a vase, a chair etc) from the real world by using the camera of my smartphone and to show a corresponding video behind that object that i am tracking, for example in a wall.

Simply, the synthetic world is going to be behind the object that i will track or only the object that I am tracking to be inside the synthetic world.

Any idea?

Thank you in advance