Firewall blocking Videostream

in practical terms, would you say on my secure network at home (which I do not share with anyone, just other devices) I could turn off the firewall, and maybe turn it on when on a public wifi for instance?

Yes. If you don't have anything enabled in Sharing, then turning on the Firewall is probably unnecessary even on a public network, but might provide some benefit in case of some zero-day (i.e. unknown) attack vector.

I suppose i could turn off the firewall completely while streaming but that kind of defeats the purpose of the firewall.

What purpose do you think the firewall is actually doing? It probably isn't doing anything but causing problems.

A firewall is a network management utility. It isolates parts of a network from specific computers, IP ranges, or other networking "locations." It isn't a "security" feature. If you are behind a NAT router, then the built-in firewall is doing nothing as nobody on the internet can see your Mac through the NAT router, unless you have poked a hole in your router and routed internet traffic to your Mac.

About the only utility in the built-in firewall is if you must have multiple sharing services enabled, and you connect your Mac to a public network. It is then simpler to turn on the firewall than to turn off all of the sharing services. A Mac with all sharing disabled doesn't need the built-in firewall enabled, even on a public network.