Hi there,
I am sorry you haven't been able to get Videos working-- based on what you say, it suggests that the videos are still using the old local storage rather than storage groups-- From a browser on your network, you can try doing this:
Replacing BackendIP with the IP of your master backend. I suspect this will return 0 objects, which means your videos are not set up in Storage Groups, but rather in local storage. On the MythTV wiki I believe there is a Video Library article that can help you with migrating to Video Storage Groups, but in short, you have to go and remove the local video media library settings in the Frontend (used to be Utilities/Setup->Setup->Media Library->Video Library->General but I suspect that has changed). On that screen, you need to clear out the local storage/artwork/etc. paths for videos, then you'll need to rescan (and potentially correct some metadata at that point). Once you're successfully getting video returns, the app should work as well.
If you get a long video list from the above API, please send it to me via email and I can take a look as see where it might be going wrong.
Thanks,
Robert