Is it possible to only allow one single application to access the network connection, excluding all other applications from generating network traffic.
Streaming video or music locally over the router seems to be interrupted by i.e. Mail, Dropbox, or update services etc. -- Hence, I would like only applications such as iTunes or Spotify to be able to use the network connection exclusively when listening to music or watching a movie...
You could create a custom rule set to achieve this using Little Snitch:
With Hands Off or/and Little Snitch, you can disable/enable the network for a specified application.
Not quite the solution you're asking for, but your router may also allow to adjust its QoS (Quality of Service) settings, which could allow you to give priority to streaming music or video over other types of internet traffic.
How you do this (and whether it's even worth trying to figure out how) will very much depend on your router and the type of UI it gives you in its configuration web app, but here's a recent guide that gives some tips to get started.
