Multicast IP Addresses Overview

Hi Andrew ,
A doubt on higher level …
I was trying to understand connection between 239.0.0.0 AND 224.0.1.0 in MULTICAST concept.
So any video server, once connects to router (so there must be some app that pump video traffic towards router) and router once configured “with respective config” , start sending traffic towards IP 239.1.1.1. And then hosts (typically equipped with an application such as VLC ) that are configured with “related host config” get this feed via that multicast router.

  1. So Is it always 239.1.1.1 or we can change this IP?
  2. where does 224.0.1.0 range comes in to scene ?

thanks.