AudioObjectGetPropertyData to get a list of input devices

Question

How do I utilize AudioObjectGetPropertyData in OS X to retrieve a list of the system\'s input devices? I currently have the following dummy code for retrieving

Answer 1

Swift 3.0 Xcode 8 Beta 5

Struggled with this for a good while but this seems to work fine for now.

func handle(_ errorCode: OSStatus) throws {
    if errorCode != kAudioHardwareNoError {
        let error = NSError(domain: NSOSStatusErrorDomain, code: Int(errorCode), userInfo: [NSLocalizedDescriptionKey : "CAError: \(errorCode)" ])
        NSApplication.shared().presentError(error)
        throw error
    }
}

func getInputDevices() throws -> [AudioDeviceID] {

    var inputDevices: [AudioDeviceID] = []

    // Construct the address of the property which holds all available devices
    var devicesPropertyAddress = AudioObjectPropertyAddress(mSelector: kAudioHardwarePropertyDevices, mScope: kAudioObjectPropertyScopeGlobal, mElement: kAudioObjectPropertyElementMaster)
    var propertySize = UInt32(0)

    // Get the size of the property in the kAudioObjectSystemObject so we can make space to store it
    try handle(AudioObjectGetPropertyDataSize(AudioObjectID(kAudioObjectSystemObject), &devicesPropertyAddress, 0, nil, &propertySize))

    // Get the number of devices by dividing the property address by the size of AudioDeviceIDs
    let numberOfDevices = Int(propertySize) / sizeof(AudioDeviceID.self)

    // Create space to store the values
    var deviceIDs: [AudioDeviceID] = []
    for _ in 0 ..< numberOfDevices {
        deviceIDs.append(AudioDeviceID())
    }

    // Get the available devices
    try handle(AudioObjectGetPropertyData(AudioObjectID(kAudioObjectSystemObject), &devicesPropertyAddress, 0, nil, &propertySize, &deviceIDs))

    // Iterate
    for id in deviceIDs {

        // Get the device name for fun
        var name: CFString = ""
        var propertySize = UInt32(sizeof(CFString.self))
        var deviceNamePropertyAddress = AudioObjectPropertyAddress(mSelector: kAudioDevicePropertyDeviceNameCFString, mScope: kAudioObjectPropertyScopeGlobal, mElement: kAudioObjectPropertyElementMaster)
        try handle(AudioObjectGetPropertyData(id, &deviceNamePropertyAddress, 0, nil, &propertySize, &name))

        // Check the input scope of the device for any channels. That would mean it's an input device

        // Get the stream configuration of the device. It's a list of audio buffers.
        var streamConfigAddress = AudioObjectPropertyAddress(mSelector: kAudioDevicePropertyStreamConfiguration, mScope: kAudioDevicePropertyScopeInput, mElement: 0)

        // Get the size so we can make room again
        try handle(AudioObjectGetPropertyDataSize(id, &streamConfigAddress, 0, nil, &propertySize))

        // Create a buffer list with the property size we just got and let core audio fill it
        let audioBufferList = AudioBufferList.allocate(maximumBuffers: Int(propertySize))
        try handle(AudioObjectGetPropertyData(id, &streamConfigAddress, 0, nil, &propertySize, audioBufferList.unsafeMutablePointer))

        // Get the number of channels in all the audio buffers in the audio buffer list
        var channelCount = 0
        for i in 0 ..< Int(audioBufferList.unsafeMutablePointer.pointee.mNumberBuffers) {
            channelCount = channelCount + Int(audioBufferList[i].mNumberChannels)
        }

        free(audioBufferList.unsafeMutablePointer)

        // If there are channels, it's an input device
        if channelCount > 0 {
            Swift.print("Found input device '\(name)' with \(channelCount) channels")
            inputDevices.append(id)
        }
    }

    return inputDevices
}