Hi, this is my first thread!
My name is Roberto and I’m italian, sorry for grammatical errors (if there are). 
My questions is this:
I can have a real-time preview in the node editor(for compositing)?
If so, how?
Recently I’m using blender and my first and my first interest are the special effects for movies. :yes:
Thanks for your attention! good luck
Enable the backdrop option on the node editor header
Add a Viewer node and connect it to the node output you want to look at
Hello and thanks for the reply!
However, if I do start the animation, it is not in real time!
If you want to play a buffered animation open the vse and add the compositor scene’s strip. In the vse preview properties turn off open gl render. You should see the compositor output. Simply play through animation once without sync. This creates a temporary animation close to real time. If you can’t buffer much then change the UI prefs for sequencer memory and allocate some more.