For what it's worth (and please note this is not complaining, just noting for development purposes) I also get the eternal spin in the Blue Iris app in Android.
I've tried in Chrome Version 66.0.3359.139 on mac and windows.
Firefox does not give me the H.264 option, so it works. Only one of my cameras is 720p, so I don't mind the low setting.
I'll try setting it in the file.