How to route audio to default speakers in Swift for macOS? - swift

Question

I have a function playing audio for a macOS swiftUI app but I want it to play the sound through the default built in speakers every single time. Does anyone know of any reliable method for this?
I've researched a lot but haven't found a solid method for macos. This is what I've tried:
AVRoutePickerView
This was only availble for ios and Mac catalyst but not macOS
Getting Device ID in AVAudioEngine
I found this code snippet but it assumes that the built in speaker device ID stays the same which it doesnt so that doesn't help.
engine = AVAudioEngine()
let output = engine.outputNode
// get the low level input audio unit from the engine:
let outputUnit = output.audioUnit!
// use core audio low level call to set the input device:
var outputDeviceID: AudioDeviceID = 51 // replace with actual, dynamic value
AudioUnitSetProperty(outputUnit,
kAudioOutputUnitProperty_CurrentDevice,
kAudioUnitScope_Global,
0,
&outputDeviceID,
UInt32(MemoryLayout<AudioDeviceID>.size))
Disabling bluetooth so the audio only goes through main speakers and not bluetooth speaker. This didn't seem the best approach so I havent' tested it.
The following is the code I have for playing sound:
func playTheSound() {
let url = Bundle.main.url(forResource: "Blow", withExtension: "mp3")
player = try! AVAudioPlayer(contentsOf: url!)
player?.play()
print("Sound was played")
//
So, any recommendations on how to route the audio to main speakers for macOS?

Answer 1

By "default built-in" I assume you actually just mean "built-in." The default speakers are the ones the audio will route to already.
The simplest solution to this that will probably always work is to route to the UID "BuiltInSpeakerDevice". For example, this does what you want:
let player = AVPlayer()
func playTheSound() {
let url = URL(filePath: "/System/Library/Sounds/Blow.aiff")
let item = AVPlayerItem(url: url)
player.replaceCurrentItem(with: item)
player.audioOutputDeviceUniqueID = "BuiltInSpeakerDevice"
player.play()
}
Note the use of AVPlayer and audioOutputDeviceUniqueID here. I'm betting this will work in approximately 100% of cases. It should even "work" if there were no built-in speakers, in that this silently fails (without crashing) if the UID doesn't exist.
But...sigh...I can't find anywhere that this is documented or any system constant for this string. And I really hate magic, undocumented strings. So, let's do it right. Besides, if we do it right, it'll work with AVAudioEngine, too. So let's get there.
First, you should always take a look at the invaluable CoreAudio output device useful methods in Swift 4. I don't know if anyone has turned this into a real framework, but this is a treasure trove of examples. The following code is a modernized version of that.
struct AudioDevice {
let id: AudioDeviceID
static func getAll() -> [AudioDevice] {
var propertyAddress = AudioObjectPropertyAddress(
mSelector: kAudioHardwarePropertyDevices,
mScope: kAudioObjectPropertyScopeGlobal,
mElement: kAudioObjectPropertyElementMain)
// Get size of buffer for list
var devicesBufferSize: UInt32 = 0
AudioObjectGetPropertyDataSize(AudioObjectID(kAudioObjectSystemObject), &propertyAddress,
0, nil,
&devicesBufferSize)
let devicesCount = Int(devicesBufferSize) / MemoryLayout<AudioDeviceID>.stride
// Get list
let devices = Array<AudioDeviceID>(unsafeUninitializedCapacity: devicesCount) { buffer, initializedCount in
AudioObjectGetPropertyData(AudioObjectID(kAudioObjectSystemObject), &propertyAddress,
0, nil,
&devicesBufferSize, buffer.baseAddress!)
initializedCount = devicesCount
}
return devices.map(Self.init)
}
var hasOutputStreams: Bool {
var propertySize: UInt32 = 256
var propertyAddress = AudioObjectPropertyAddress(
mSelector: kAudioDevicePropertyStreams,
mScope: kAudioDevicePropertyScopeOutput,
mElement: kAudioObjectPropertyElementMain)
AudioObjectGetPropertyDataSize(id, &propertyAddress, 0, nil, &propertySize)
return propertySize > 0
}
var isBuiltIn: Bool {
transportType == kAudioDeviceTransportTypeBuiltIn
}
var transportType: AudioDevicePropertyID {
var deviceTransportType = AudioDevicePropertyID()
var propertySize = UInt32(MemoryLayout<AudioDevicePropertyID>.size)
var propertyAddress = AudioObjectPropertyAddress(
mSelector: kAudioDevicePropertyTransportType,
mScope: kAudioObjectPropertyScopeGlobal,
mElement: kAudioObjectPropertyElementMain)
AudioObjectGetPropertyData(id, &propertyAddress,
0, nil, &propertySize,
&deviceTransportType)
return deviceTransportType
}
var uid: String {
var propertySize = UInt32(MemoryLayout<CFString>.size)
var propertyAddress = AudioObjectPropertyAddress(
mSelector: kAudioDevicePropertyDeviceUID,
mScope: kAudioObjectPropertyScopeGlobal,
mElement: kAudioObjectPropertyElementMain)
var result: CFString = "" as CFString
AudioObjectGetPropertyData(id, &propertyAddress, 0, nil, &propertySize, &result)
return result as String
}
}
And with that in place, you can fetch the first built-in output device:
player.audioOutputDeviceUniqueID = AudioDevice.getAll()
.first(where: {$0.hasOutputStreams && $0.isBuiltIn })?
.uid
Or you can use your AVAudioEngine approach if you want more control (note difference between uid and id here):
let player = AVAudioPlayerNode()
let engine = AVAudioEngine()
func playTheSound() {
let output = engine.outputNode
let outputUnit = output.audioUnit!
var outputDeviceID = AudioDevice.getAll()
.first(where: {$0.hasOutputStreams && $0.isBuiltIn })!
.id
AudioUnitSetProperty(outputUnit,
kAudioOutputUnitProperty_CurrentDevice,
kAudioUnitScope_Global,
0,
&outputDeviceID,
UInt32(MemoryLayout<AudioDeviceID>.size))
engine.attach(player)
engine.connect(player, to: engine.outputNode, format: nil)
try! engine.start()
let url = URL(filePath: "/System/Library/Sounds/Blow.aiff")
let file = try! AVAudioFile(forReading: url)
player.scheduleFile(file, at: nil)
player.play()
}