Playing periodic audio in background using AVFoundation - facing audio session startup failure

Hello everyone,

I’m new to Swift development and have been working on an audio module that plays a specific sound at regular intervals - similar to a workout timer that signals switching exercises every few minutes.

Following AVFoundation documentation, I’m configuring my audio session like this:

let session = AVAudioSession.sharedInstance()

try session.setCategory(
  .playback,
  mode: .default,
  options: [.interruptSpokenAudioAndMixWithOthers, .duckOthers]
)

self.engine.attach(self.player)
self.engine.connect(self.player, to: self.engine.outputNode, format: self.audioFormat)

try? session.setActive(true)

When it’s time to play cues, I schedule playback on a DispatchQueue:

// scheduleAudio uses DispatchQueue
self.scheduleAudio(at: interval.start) {
    do {
        try audio.engine.start()
        audio.node.play()

        for sample in interval.samples {
            audio.node.scheduleBuffer(sample.buffer, at: AVAudioTime(hostTime: sample.hostTime))
        }
    } catch {
        print("Audio activation failed: \(error)")
    }
}

This works perfectly in the foreground. But once the app goes into the background, the scheduled callback runs, yet the audio engine fails to start, resulting in an error with code 561015905.

Interestingly, if the app is already playing audio before going to the background, the scheduled sounds continue to play as expected.

I have added the required background audio mode to my Info plist file by including the key UIBackgroundModes with the value audio.

Is there anything else I should configure? What is the best practice to play periodic audio when the app runs in the background? How do apps like turn-by-turn navigation handle continuous audio playback in the background?

Any advice or pointers would be greatly appreciated!