Moving from VR back to the "real world" (passthrough camera)?

Hi,

I'm pretty new to Unity so it might be a a pretty obvious thing - but if i have a movie projected on a sphere which at the end of it i want to trigger the phone's camera (or even blend between the two, if some part of the movie has an alpha) so the user could "go back to the real world" for a certain amount of time, and then blend (again, using the movie's alpha channel) into another video. 

What would be the procedure for achieving that?

Thanks!