There are not many of us who run OH in Docker. There are many fewer of us who run it using TTS. what ever is wrong here is going to be a networking issue between the containers. You might get better support on a Docker container.
But I can say the following:
Port 8080 is the HTTP port. For HTTPS you need to use port 8443.
If you haven’t configure the container to use --net=host or exported and mapped the ports in your docker run command, openHAB is no accessible outside the docker container network.
I feared that almost no one uses OH in a Docker…
But should I be able to access the file by copy the URL to the Webbrowser?
If so then the problem would lay by the OH network config.
I think it has something to do with the proxy. The LMS will receive the URL form OH and does it send the URL directly to the Player so that the player needs to access the stream by himself or will it stream the content to the player?
I might found a Bug or the Problem:
I’ve saw the the KODI binding has also a callback url and this can be set by clicking the pen Icon see Image.
However the Squeezbox Binding has no such Icon although in the Binding.xml it is mentioned like in the Kodi binding.xml…