Getting/setting volume, balance, mute using CoreAudio (inspired by https://github.com/digital-pers0n/keepQuiet)

CoreAudio.swift

import CoreAudio
import AudioToolbox

let defaultDeviceProp = AudioObjectPropertyAddress(
  mSelector: kAudioHardwarePropertyDefaultOutputDevice,
  mScope: kAudioObjectPropertyScopeGlobal,
  mElement: kAudioObjectPropertyElementMaster)

let masterVolumeProp = AudioObjectPropertyAddress(
  mSelector: kAudioHardwareServiceDeviceProperty_VirtualMasterVolume,
  mScope: kAudioDevicePropertyScopeOutput,
  mElement: kAudioObjectPropertyElementMaster)

let balanceProp = AudioObjectPropertyAddress(
  mSelector: kAudioHardwareServiceDeviceProperty_VirtualMasterBalance,
  mScope: kAudioDevicePropertyScopeOutput,
  mElement: kAudioObjectPropertyElementMaster)

let muteVolumeProp = AudioObjectPropertyAddress(
  mSelector: kAudioDevicePropertyMute,
  mScope: kAudioDevicePropertyScopeOutput,
  mElement: kAudioObjectPropertyElementMaster)


enum AudioPropertyError : Error {
  case NoProperty
  case PropertyNotSettable
  case GetPropertyData(OSStatus)
  case SetPropertyData(OSStatus)
  case EmptyResult
}

struct AudioProperty<T> {
  let emptyValue: T?
  let device: AudioDeviceID
  let prop: AudioObjectPropertyAddress

  // For numerical values if we don't initialize 'result: T?' to non-nil
  // value we'll get .EmptyResult error if the value is zero.
  init(device: AudioDeviceID?, emptyValue: T?, prop: AudioObjectPropertyAddress) {
    self.emptyValue = emptyValue
    self.device = device ?? UInt32(kAudioObjectSystemObject)
    self.prop = prop
  }

  func get() -> Result<T, AudioPropertyError> {
    var p = prop
    if (!AudioObjectHasProperty(device, &p)) {
      return .failure(.NoProperty)
    }

    var size = UInt32(MemoryLayout<T>.size)
    var result: T? = emptyValue
    let error = AudioObjectGetPropertyData(device, &p, 0, nil, &size, &result)

    if (error != noErr) {
      return .failure(.GetPropertyData(error))
    }

    if let result = result {
      return .success(result)
    }

    return .failure(.EmptyResult)
  }

  func set(_ newValue: T) -> Result<T, AudioPropertyError> {
    var p = prop
    if (!AudioObjectHasProperty(device, &p)) {
      return .failure(.NoProperty)
    }

    var settable: DarwinBoolean = false
    var error = AudioObjectIsPropertySettable(device, &p, &settable)
    if (error != noErr) {
      return .failure(.PropertyNotSettable)
    }

    let size = UInt32(MemoryLayout<T>.size)
    var value = newValue
    error = AudioObjectSetPropertyData(device, &p, 0, nil, size, &value)
    if (error != noErr) {
      return .failure(.SetPropertyData(error))
    }

    return .success(value)
  }
}

let device = AudioProperty<AudioDeviceID>(device: nil, emptyValue: nil, prop: defaultDeviceProp)
let volume = AudioProperty<Float>(device: device.get().get(), emptyValue: 0, prop: masterVolumeProp)
let balance = AudioProperty<Float>(device: device.get().get(), emptyValue: 0, prop: balanceProp)
let mute = AudioProperty<UInt32>(device: device.get().get(), emptyValue: 0, prop: muteVolumeProp)
device.get()
volume.get()
balance.get()
mute.get()

balance.set(0.58)
volume.set(0.3)