Ah... your "independent playback progress/state class" is another state machine, just better with an architecture that suits your use case. "Full state machine"

Ah... your "independent playback progress/state class" is another state machine, just better with an architecture that suits your use case. "Full state machine" is a misnomer and common misunderstanding of the power of state machines. Any state machine bordering on complexity that is hard to manage can be broken into multiple smaller, easier to grasp and manage state machines. And state machines transparently integrate with functional programming, so any ideas contrary to that is yet another misunderstanding of them.