How can i put the video fixed on the ImageTarget no matter what size the image is?

When I was focusing on the imagge on my Screen Computer, it's doing very well as i want. But when I was trying to do it again on the same tag but on the magazine with the size a little bit small, it's coming out of the imagge and it is trembling. So I want it can keep in the same size I will focus and not trembling. How can i put the video fixed on the ImageTarget no matter what size the image is?