set of <code>streamDescriptors</code> 
  to users in the room. Collaboration components such as WebcamSubscriber or AudioSubscriber
  use <code>streamDescriptors</code> to directly access the raw streams and may be thought
  of as control metadata for indicating the presence and current state of streams in a room.
  <p>
  
  StreamDescriptors can be accessed through the StreamManager's methods, and StreamManager's 
  events will notify of any changes to  the set of <code>streamDescriptors</code>.
  
  <p></