设置猪模式后无法播放声音

Question

我尝试将带有AVAudioEngine和AVAudioPlayerNode的音频文件播放到USB设备(DAC(。当我将设备设置为猪模式时，声音不会播放，但没有猪模式时效果很好。

我也尝试使用AVAudioPlayer，但它也不起作用。

有人知道为什么以及如何解决这个问题吗？

如果我将设备ADI-2设置为Hog模式，系统会将默认设备设置为另一个设备Meridian并在其上播放声音。我找不到在Hog模式ADI-2下在设备上播放声音的方法(见下图(。

无hog模式

hog模式

import Cocoa
import AVFoundation
class ViewController: NSViewController {
let audioEngine = AVAudioEngine()
let playerNode = AVAudioPlayerNode()
override func viewDidLoad() {
super.viewDidLoad()
do {
let outputDevice = AudioDevice.defaultOutputDevice()
guard let url = Bundle.main.url(forResource: "file", withExtension: "mp3") else { return }
let audioFile = try AVAudioFile(forReading: url)
outputDevice.setHogMode() // without this line, audio file is played.
audioEngine.attach(playerNode)
audioEngine.connect(playerNode, to: audioEngine.mainMixerNode, format: audioFile.processingFormat)
try audioEngine.start()
playerNode.scheduleFile(audioFile, at: nil, completionHandler: nil)
playerNode.play()
} catch let error {
print(error.localizedDescription)
}
}
}

class AudioDevice {
var id: AudioDeviceID
init(deviceID: AudioDeviceID) {
self.id = deviceID
}
func setHogMode() -> Bool {
guard hogModePID() != pid_t(ProcessInfo.processInfo.processIdentifier) else { return false }
return toggleHogMode()
}
func unsetHogMode() -> Bool {
guard hogModePID() == pid_t(ProcessInfo.processInfo.processIdentifier) else { return false }
return toggleHogMode()
}
private func toggleHogMode() -> Bool {
let address = AudioObject.address(selector: kAudioDevicePropertyHogMode)
var newValue: UInt32 = 1
let status = AudioObject.setPropertyData(id, address: address, andValue: &newValue)
return noErr == status
}
private func hogModePID() -> pid_t? {
let address = AudioObject.address(selector: kAudioDevicePropertyHogMode)
var pid = pid_t()
let status = AudioObject.getPropertyData(id, address: address, andValue: &pid)
return noErr == status ? pid : nil
}
}
extension AudioDevice {
class func defaultOutputDevice() -> AudioDevice {
let address = AudioObject.address(selector: kAudioHardwarePropertyDefaultSystemOutputDevice)
var deviceId = AudioDeviceID()
let status = AudioObject.getPropertyData(AudioObjectID(kAudioObjectSystemObject), address: address, andValue: &deviceId)
if status != noErr {
print("OSStatus error (status) (defaultOutputDevice)")
}
return AudioDevice(deviceID: deviceId)
}
}

class AudioObject {
class func address(selector: AudioObjectPropertySelector, scope: AudioObjectPropertyScope = kAudioObjectPropertyScopeGlobal, element: AudioObjectPropertyElement = kAudioObjectPropertyElementMaster) -> AudioObjectPropertyAddress {
return AudioObjectPropertyAddress(mSelector: selector, mScope: scope, mElement: element)
}
class func getPropertyData<T>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, andValue value: inout T) -> OSStatus {
var theAddress = address
var size = UInt32(MemoryLayout<T>.size)
let status = AudioObjectGetPropertyData(objectID, &theAddress, UInt32(0), nil, &size, &value)
return status
}
class func getPropertyDataSize<Q>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, qualifierDataSize: UInt32?, qualifierData: inout [Q], andSize size: inout UInt32) -> (OSStatus) {
var theAddress = address
return AudioObjectGetPropertyDataSize(objectID, &theAddress, qualifierDataSize ?? UInt32(0), &qualifierData, &size)
}
class func getPropertyDataSize<Q>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, qualifierDataSize: UInt32?, qualifierData: inout Q, andSize size: inout UInt32) -> (OSStatus) {
var theAddress = address
return AudioObjectGetPropertyDataSize(objectID, &theAddress, qualifierDataSize ?? UInt32(0), &qualifierData, &size)
}
class func getPropertyDataSize(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, andSize size: inout UInt32) -> (OSStatus) {
var nilValue: ExpressibleByNilLiteral?
return getPropertyDataSize(objectID, address: address, qualifierDataSize: nil, qualifierData: &nilValue, andSize: &size)
}
class func getPropertyDataArray<T, Q>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, qualifierDataSize: UInt32?, qualifierData: inout Q, value: inout [T], andDefaultValue defaultValue: T) -> OSStatus {
var size = UInt32(0)
let sizeStatus = getPropertyDataSize(objectID, address: address, qualifierDataSize: qualifierDataSize, qualifierData: &qualifierData, andSize: &size)
if noErr == sizeStatus {
value = [T](repeating: defaultValue, count: Int(size) / MemoryLayout<T>.size)
} else {
return sizeStatus
}
var theAddress = address
let status = AudioObjectGetPropertyData(objectID, &theAddress, qualifierDataSize ?? UInt32(0), &qualifierData, &size, &value)
return status
}
class func getPropertyDataArray<T, Q>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, qualifierDataSize: UInt32?, qualifierData: inout [Q], value: inout [T], andDefaultValue defaultValue: T) -> OSStatus {
var size = UInt32(0)
let sizeStatus = getPropertyDataSize(objectID, address: address, qualifierDataSize: qualifierDataSize, qualifierData: &qualifierData, andSize: &size)
if noErr == sizeStatus {
value = [T](repeating: defaultValue, count: Int(size) / MemoryLayout<T>.size)
} else {
return sizeStatus
}
var theAddress = address
let status = AudioObjectGetPropertyData(objectID, &theAddress, qualifierDataSize ?? UInt32(0), &qualifierData, &size, &value)
return status
}
class func getPropertyDataArray<T>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, value: inout [T], andDefaultValue defaultValue: T) -> OSStatus {
var nilValue: ExpressibleByNilLiteral?
return getPropertyDataArray(objectID, address: address, qualifierDataSize: nil, qualifierData: &nilValue, value: &value, andDefaultValue: defaultValue)
}
class func setPropertyData<T>(_ objectID: AudioObjectID, address: AudioObjectPropertyAddress, andValue value: inout T) -> OSStatus {
var theAddress = address
let size = UInt32(MemoryLayout<T>.size)
let status = AudioObjectSetPropertyData(objectID, &theAddress, UInt32(0), nil, size, &value)
return status
}
}

Answer 1

所以我自己从来没有真正使用过AVAudioEngine，但我想如果你想让它使用特定的设备，你需要配置它来这样做(我在代码中没有看到(

我相信你看到的行为是：

• 默认情况下，AVAudioEngine将使用系统默认设备
• 通过在一个恰好是当前系统默认设备的设备上采用hog模式，该设备就不能再是默认设备了——你是在间接地更改默认设备
• 由于没有明确指定输出设备，因此播放使用当前系统默认设备

看起来有一个类似的问题可能会有所帮助(尽管答案是Objective-C(：设置音频引擎输入和输出设备

就hog模式而言，它可能不太适合用户(并且可能主要用于需要使用不可混合格式的情况(。