Hy everyone!
I’ve got a question about reflection in glass:
I made a glass-break animation which I wanna put in a video. So I set as reference video AND with the node editor my movie but it has no affect on the glass reflection.
On the screenshot you can see how I tried it, I’ve got the background video running with the animation but you can’t see any reflection from the video in the glass splitters. It’s just gray.
What can I do?
Well if your adding the movie in the compositor, of course it won’t affect the reflection.
The reflection is calculated during render, based on whats in the render. So unless you have your video somehow as an environment in Blender, once the image is rendered, all lighting is calculated.
You may want to look at using a HDRi or spherical panorama (you could make one of the film location) or to render your objects with some transparency rather than refraction, so when you compose it you can see some of the image behind.
Your film is transparent, but glass is not ‘transparent’ it is refracted, meaning once calculated by the world colour, it can’t change later in composition.
Thank you so much! HDRi was the word!! 
For anybody who got the same question and ended up here:
-> Go to world properties
-> Go to “Surface”
-> Select “Background” as Surface
-> Choose “Environment Texture” as Color
-> Insert your movie file
-> Adjust settings if needed
