Using MPNowPlayingInfoCenter without actually playing audio

Question

I am trying to build an iOS app which controls a music player which runs on a seperate machine. I would like to use the MPNowPlayingInfoCenter for inspecting and controlling this player. As far as I can tell so far, the app actually has to output audio for this to work (see also this answer).

However, for instance, the Spotify app is actually capable of doing this without playing audio on the iOS device. If you use Spotify Connect to play the audio on a different device, the MPNowPlayingInfoCenter still displays the correct song and the controls are functional.

What's the catch here? What does one (conceptually) have to do to achieve this? I can think of continuously emitting a "silent" audio stream, but that seams a bit brute-force.

Rob Napier · Answer 1 · 2018-03-09T13:50:38.343

Streaming silence will work, but you don't need to stream it all the time. Just long enough to send your Now Playing info. Using AVAudioPlayer, I've found approaches as short as this will send the data (assuming the player is loaded with a 1s silent audio file):

    player.play()

    let nowPlayingInfoCenter = MPNowPlayingInfoCenter.default()

    nowPlayingInfoCenter.nowPlayingInfo = [...]

    player.stop()

I was very surprised this worked within a single event loop. Any other approach to playing silence seems to work as well. Again, it can be very brief (in fact the above code in my tests doesn't even get as far as playing the silence).

I'm very interested in whether this works reliably for other people, so please comment if you make discoveries about it.

I've explored the Spotify app a bit. I'm not 100% certain if this is the same technique they're using. They're able to mix with other audio somehow. So you can be playing local audio on the phone and also playing Spotify Connect to some other device, and the "Now Playing" info will kind of stomp on each other. For my purposes, that would actually be better, but I haven't been able to duplicate it. I still have to make the audio session non-mixable for at least a moment (so you get ~ 1s audio drop if you're playing local audio at the same time). I did find that the Spotify app was not highly reliable about playing to my Connect device when I was also playing other audio locally. Sometimes it would get confused and switch around where it wanted to play. (Admittedly this is a bizarre use case; I was intentionally trying to break it to figure out how they're doing it.)

EDIT: I don't believe Spotify is actually doing anything special here. I think they just play silent audio. I think getting two streams playing at the same time has to do with AirPlay rather than Spotify (I can't make it happen with Bluetooth, only AirPlay).

Using MPNowPlayingInfoCenter without actually playing audio

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