Giving it either a long (2.5hr) video, or a non-youtube URL (e.g. an invidious link) appears to leave it spinning forever - no error message.
As for non-Youtube URL: I indeed do not handle that error right now :D. Thanks so much for bringing it up!
This 1hr video works (but I note you don't seem to be caching the output?) https://www.youtube.com/watch?v=0s9fpFPAC94