How can I allow background music to continue playing while my app still plays its sounds while using Swift

I created an app and I am attempting to allow the user to continue to listen to their music while playing my game, but whenever they hit "play" and the ingame sounds occur it will stop the background music. I am developing on iOS using Swift. Here is a piece of the code that initiates the ingame sounds.

func playSpawnedDot() {
    var alertSound: NSURL = NSURL(fileURLWithPath: NSBundle.mainBundle().pathForResource("spawnDot", ofType: "mp3")!)!
    var error:NSError?
    audioPlayer = AVAudioPlayer(contentsOfURL: alertSound, error: &error)
    audioPlayer.prepareToPlay()
        
    if volumeBool {
        audioPlayer.play()
    }
}

You need to set the AVAudioSession category, with one of the following value: https://developer.apple.com/library/ios/documentation/AVFoundation/Reference/AVAudioSession_ClassReference/index.html (AVAudioSession Class Reference).

The default value is set to AVAudioSessionCategorySoloAmbient. As you can read : > [...] using this category implies that your app’s audio is nonmixable—activating your session will interrupt any other audio sessions which are also nonmixable. To allow mixing, use the AVAudioSessionCategoryAmbient category instead.

You have to change the category, before you play your sound. To do so :

AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient, error: nil)
AVAudioSession.sharedInstance().setActive(true, error: nil)

You don't need to call those line each time you play the sound. You might want to do it only once.

Swift 4 version:

try? AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient)
try? AVAudioSession.sharedInstance().setActive(true)

This is how I do it in Swift 3.0

var songPlayer : AVAudioPlayer?	 	 	

func SetUpSound() {
		
		
		if let path = Bundle.main.path(forResource: "TestSound", ofType: "wav") {
			let filePath = NSURL(fileURLWithPath:path)
			songPlayer = try! AVAudioPlayer.init(contentsOf: filePath as URL)
			songPlayer?.numberOfLoops = -1 //logic for infinite loop
			songPlayer?.prepareToPlay()
			songPlayer?.play()
		}

        let audioSession = AVAudioSession.sharedInstance()
        try!audioSession.setCategory(AVAudioSessionCategoryPlayback, with: AVAudioSessionCategoryOptions.duckOthers) //Causes audio from other sessions to be ducked (reduced in volume) while audio from this session plays  
}

You can see more of AVAudioSessionCategoryOptions here: https://developer.apple.com/reference/avfoundation/avaudiosessioncategoryoptions

Here's what I am using for Swift 2.0:

let sess = AVAudioSession.sharedInstance()
if sess.otherAudioPlaying {
    _ = try? sess.setCategory(AVAudioSessionCategoryAmbient, withOptions: .DuckOthers)
    _ = try? sess.setActive(true, withOptions: [])
}

Please note that you can replace .DuckOthers with [] if you don't want to lower background music and instead play on top to it.

lchamp's solution worked perfectly for me, adapted for Objective-C:

[[AVAudioSession sharedInstance] setCategory:AVAudioSessionCategoryAmbient error:nil];
[[AVAudioSession sharedInstance] setActive:YES error:nil];

**

Updated for Swift 3.0

**

The name of the sound I am playing is shatter.wav

func shatterSound() {
    if let soundURL = Bundle.main.url(forResource: "shatter", withExtension: "wav") {
        var mySound: SystemSoundID = 0
        AudioServicesCreateSystemSoundID(soundURL as CFURL, &mySound)
        AudioServicesPlaySystemSound(mySound);
    }
}

Then where ever you want to play the sound call

shatterSound()

Since they can't seem to make up their minds from version to version. Here it is in Swift 5.0

do{
   try AVAudioSession.sharedInstance().setCategory(.ambient)
   try AVAudioSession.sharedInstance().setActive(true, options: .notifyOthersOnDeactivation)
} catch {
   NSLog(error.localizedDescription)
}

If you want to play an alert sound:

public func playSound(withFileName fileName: String) {
    
    if let soundUrl = Bundle.main.url(forResource: fileName, withExtension: "wav") {
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient, with:[.duckOthers])
            try AVAudioSession.sharedInstance().setActive(true)
            
            var soundId: SystemSoundID = 0
            
            AudioServicesCreateSystemSoundID(soundUrl as CFURL, &soundId)
            AudioServicesAddSystemSoundCompletion(soundId, nil, nil, { (soundId, clientData) -> Void in
                AudioServicesDisposeSystemSoundID(soundId)
                do {
                    // This is to unduck others, make other playing sounds go back up in volume
                    try AVAudioSession.sharedInstance().setActive(false)
                } catch {
                    DDLogWarn("Failed to set AVAudioSession to inactive. error=\(error)")
                }
            }, nil)
            
            AudioServicesPlaySystemSound(soundId)
        } catch {
            DDLogWarn("Failed to create audio player. soundUrl=\(soundUrl) error=\(error)")
        }
    } else {
        DDLogWarn("Sound file not found in app bundle. fileName=\(fileName)")
    }
}

And if you want to play music:

import AVFoundation

var audioPlayer:AVAudioPlayer?

public func playSound(withFileName fileName: String) {
    
    if let soundUrl = Bundle.main.url(forResource: fileName, withExtension: "wav") {
        do {
            try AVAudioSession.sharedInstance().setCategory(AVAudioSessionCategoryAmbient, with:[.duckOthers])
            try AVAudioSession.sharedInstance().setActive(true)
   
            let player = try AVAudioPlayer(contentsOf: soundUrl)
            player.delegate = self
            player.prepareToPlay()
            DDLogInfo("Playing sound. soundUrl=\(soundUrl)")
            player.play()
            // ensure the player does not get deleted while playing the sound
            self.audioPlayer = player
        } catch {
            DDLogWarn("Failed to create audio player. soundUrl=\(soundUrl) error=\(error)")
        }
    } else {
        DDLogWarn("Sound file not found in app bundle. fileName=\(fileName)")
    }
}

func audioPlayerDidFinishPlaying(_ player: AVAudioPlayer, successfully flag: Bool) {
    self.audioPlayer?.stop()
    do {
        // This is to unduck others, make other playing sounds go back up in volume
        try AVAudioSession.sharedInstance().setActive(false)
    } catch {
        DDLogWarn("Failed to set AVAudioSession inactive. error=\(error)")
    }
}

For Swift (Objective-C like this too)

you can use this link for best answer and if you don't have any time for watching 10 minutes the best action is that you just copy below code in your AppDelegate in didFinishLaunchingWithOptions and then select your project's target then go to Capabilities and at last in Background modes check on Audio, AirPlay and Picture in Picture

func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey: Any]?) -> Bool {
    // Override point for customization after application launch.
    
    let session = AVAudioSession.sharedInstance()
    do {
        try session.setCategory(AVAudioSessionCategoryPlayback)
    }
    catch {
        
    }
}

I didn't think that just setting the AVAudioSession to AVAudioSessionCategoryOptions.duckOthers would work, but it did. Here is my full code to help the rookies like myself.

Swift 4 - Full Example:

var audioPlayer = AVAudioPlayer()


func playSound(sound: String){
    let path = Bundle.main.path(forResource: sound, ofType: nil)!
    let url = URL(fileURLWithPath: path)
    
    let audioSession = AVAudioSession.sharedInstance()
    try!audioSession.setCategory(AVAudioSessionCategoryPlayback, with: AVAudioSessionCategoryOptions.duckOthers)
    
    do {
        audioPlayer = try AVAudioPlayer(contentsOf: url)
        audioPlayer.play()
    } catch {
        print("couldn't load the file")
    }
}

I still need to figure out setActive (I was looking at this blog post) but the audio stops ducking when I leave the app, so it works for my app.

Swift 5 Version based on lchamp`s answer.

try? AVAudioSession.sharedInstance().setCategory(AVAudioSession.Category.ambient)
try? AVAudioSession.sharedInstance().setActive(true)

This works perfectly for me on iOS 14.4 and Swift 5. It's a bit different answer from others by using the .duckOthers option (and you can also mix directly with sound if you'd like with .mixWithOthers), but it works perfectly while music plays. It will lower the volume of the music, play the "beep" sound, and then raise the music volume back up to normal. It also captures error data using Google Firebase Crashlytics if there is an issue, and tries to raise the volume to normal even on an error.

This code will also work perfectly on the first, and all other, plays of your sound without it stopping the music ever.

func playSound() {
    do {
        if let path = Bundle.main.path(forResource: "beep", ofType: "mp3") {
            try AVAudioSession.sharedInstance().setCategory(.playback, mode: .default, options: .duckOthers)
            try AVAudioSession.sharedInstance().setActive(true)
            
            let filePath = NSURL(fileURLWithPath:path)
            songPlayer = try AVAudioPlayer.init(contentsOf: filePath as URL)
            songPlayer?.numberOfLoops = 0
            songPlayer?.prepareToPlay()
            songPlayer?.play()
            
            try AVAudioSession.sharedInstance().setActive(false)
        }
    } catch (let error) {
        try? AVAudioSession.sharedInstance().setActive(false)
        Crashlytics.crashlytics().setCustomValue(error.localizedDescription, forKey: "audio_playback_error")
    }
}

An important thing the others answers do not have is that you need to call false with the .notifyOthers flag when deactivating:

try AVAudioSession.sharedInstance().setActive(false, options: .notifyOthersOnDeactivation)

The reason for this is that other apps playing music in the background will know when to turn their audio back on when you deactivate yours. Otherwise your background music won't turn back on if you turned off your session.