In iOS, you can remotely-control a HomePod via Control Center, the Music app, and Apple’s Podcasts app.
If a third-party developer wanted to send an iTunes podcast episode or an Apple Music item to a HomePod, could they build similar in-app controls like Music or Podcasts?
(Yes, I know that I can use AirPlay to stream audio to a HomePod - but that’s not quite the same as the UI shown below...)
I expect that there’s not a way for a third-party app to implement such a control - but I’d love to know if it is!
AFAIK there's no public API for this. I think it's currently implemented by the private framework MediaRemote.framework.