设置Hog模式后无法播放声音答案

【问题标题】：Can't play sound after setting Hog mode设置Hog模式后无法播放声音
【发布时间】：2020-11-25 20:09:32
【问题描述】：

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 Hog 模式时，声音不会播放，但在没有 Hog 模式时效果很好。

我也尝试使用AVAudioPlayer，但它也不起作用。

有谁知道为什么以及如何解决这个问题？

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。我找不到在设备上以 hog 模式播放声音的方法 ADI-2（见下图）。

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
    }
}

【问题讨论】：

我不知道，只是一些深思熟虑 - 看看 MythTV 和 Kodi 源代码 - 他们在设置 hog 模式之前禁用自动 hog，还有一些驱动程序不使用的 cmets '不支持它或者他们有问题，他们在设置猪模式后也会禁用混合，...
我设法用audioOutIOProcID 和AudioDeviceCreateIOProcID 播放声音。我必须使用低级 API 还是可以在 hog 模式下使用 AVAudioEngine 播放音频文件？

标签： swift macos avfoundation core-audio audiotoolbox

【解决方案1】：

所以我自己从来没有真正使用过AVAudioEngine，但我猜如果你想让它使用特定的设备，你需要对其进行配置（我在代码中没有看到）

我相信您看到的行为是：

默认AVAudioEngine会使用系统默认设备
通过在恰好是当前系统默认设备的设备上采用 hog 模式，该设备不能再成为默认设备 - 您正在间接更改默认设备。
由于没有明确指定输出设备，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）： Set AVAudioEngine Input and Output Devices

就 hog 模式而言，它可能被认为不是非常用户友好（并且可能主要用于您需要使用不可混合格式时）。

【讨论】：