> The most reliable way is to rely on your system firewall to prompt you to open up a port when an application binds to it...But the whole point it to take the router out of the loop for this, and only use it as a coarse firewall.

I don't trust, and doubt I'll ever trust, the firewall on my Smart TV, even if it had one. That's because I don't trust that it'll ever receive timely security updates. So I must use [the firewall on] a central router.