Sup. The ustreamer developer here. I am glad that you use my software, but just in case I want to warn those who want to use RPi CSI cameras: it doesn't work with ustreamer. The reason is that these cameras use their own specific non-v4l2 driver. It is possible to configure them as v4l2, but this requires research and I have not yet addressed this issue. So if you don't want any problems, use regular USB cameras.

Quick answers to old questions:

• 0.0.0.0 is a special address that means "listen all ipv4 interfaces". If you choose this option, you can connect to the streamer via the ip address of your network card or localhost (127.0.0.1).
• You can't listen to port 80 unless you are root or have the CAP_NET_BIND_SERVICE capability (blah-blah-blah the network magic). If you want to run ustreamer via systemd on port 80 under non-root user, you need to add a parameter AmbientCapabilities=CAP_NET_BIND_SERVICE to the Service section
• Use the HW encoder: almost all cameras support it.
• If you're afraid that someone will see your video, use password authorization. It's better than nothing.

PS: I was just passing by, so if you need any help, go to discord, the link is in the ustreamer repository on github.