I didn't see that you have continue to maintain this addon. Great news !!
Because some users ask for playing theme when browsing movie library :
I was playing with the original code yesterday and I was able to play theme for a movie or for a movie set (when movies are grouped into movie sets).
This morning, I'm trying your mod but I didn't see anything in the log telling me that theme.mp3 was found and playing (I'm doing my test at my office so I have mute my laptop
When using my mod, theme.mp3 is playing when browsing level 1 library and continue playing when entering level 2 movie set (seems to work only for moviesets at the moment because when browsing Avatar, wrong path is used : C:\Videos\Films\themes.mp3 or C:\Videos\theme.mp3) :
My tvtunes_backend.py :
My library :
My files :
You can use my code if you want.