使用AVSampleBufferAudioRenderer播放音频时如何更改输出设备？

Question

我正在从代码中接收到的输入渲染音频：

...
let bufferRenderSyncer = AVSampleBufferRenderSynchronizer() 
let bufferRenderer = AVSampleBufferAudioRenderer()
...
func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
            bufferRenderer.enqueue(sampleBuffer)
            
            if bufferRenderSyncer.rate == 0 {
                bufferRenderSyncer.setRate(1, time: sampleBuffer.presentationTimeStamp)
            }
        }
...

无论有没有耳机，它都可以很好地工作（我在 iPhone 或耳机上对麦克风讲话，并从相关扬声器（例如 iPhone 或耳机上）听到自己的声音）

但我需要在耳机上使用麦克风，并且输出设备可以在耳机、扬声器或其他连接的耳机（airpods）之间切换

我没有找到任何消息来源说明如何使用 bufferRenderer 更改输出设备（默认）..有什么建议吗？

Answer 1

当我们在 macOS 上使用 AVSampleBufferAudioRenderer 时，要更改输出设备，我们需要手动更新

audioOutputDeviceUniqueID

属性。

看一下 AVSampleBufferAudioRenderer 的这个仅 macOS 实例属性：

默认情况下，AVSampleBufferAudioRenderer 使用默认的音频输出设备（即audioOutputDeviceUniqueID 为nil）。

但是，如果默认输出设备发生更改（例如，当用户插入耳机或选择不同的输出设备时），渲染器不会自动切换到新设备。手动将 audioOutputDeviceUniqueID 设置为新设备的唯一 ID 可确保音频继续通过正确的输出播放。

我正好在Apple平台上开发视频播放器，因为我们在iOS/iPad/tvOS平台上有AVAudioSession API来处理音频路由更改，但macOS上没有这样的API，这是我用来切换音频输出的代码设备：

import CoreAudio
import AudioToolbox
import AVFoundation

/// A Event Handler for Audio Route change events from macOS
class AudioRouteChangeHandler {
    
    private var audioRenderer: AVSampleBufferAudioRenderer
    
    private var callback: AudioObjectPropertyListenerBlock!
    
    private let queue: DispatchQueue
    
    init(renderer: AVSampleBufferAudioRenderer, queue: DispatchQueue) {
        self.audioRenderer = renderer
        self.queue = queue
        self.callback = { [weak self] ( _, _ ) in
            guard let self else { return }
            handleAudioRouteChange()
        }
        registerAudioRouteChangeListener()
    }
    
    
    private func registerAudioRouteChangeListener() {
        var pAddrs = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        
        let systemObjectId = AudioObjectID(kAudioObjectSystemObject)
        let status = AudioObjectAddPropertyListenerBlock(systemObjectId,
                                                         &pAddrs,
                                                         queue,
                                                         callback)
    }
    
    deinit {
        var propertyAddress = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        let systemObjectID = AudioObjectID(kAudioObjectSystemObject)
        AudioObjectRemovePropertyListenerBlock(systemObjectID, &propertyAddress, queue, callback)
    }
}


extension AudioRouteChangeHandler {
    func handleAudioRouteChange() {
        debugPrint("Audio route changed")
        // Retrieve the new default output device's UID
        if let deviceUID = getDefaultOutputDeviceUID() {
            // Update the audioRenderer's audioOutputDeviceUniqueID
            updateAudioRendererDeviceUID(deviceUID)
        } else {
            debugPrint("Failed to get default output device UID")
        }
    }
    
    func getDefaultOutputDeviceUID() -> String? {
        var deviceID = AudioDeviceID(0)
        var propertyAddress = AudioObjectPropertyAddress(
            mSelector: kAudioHardwarePropertyDefaultOutputDevice,
            mScope: kAudioObjectPropertyScopeGlobal,
            mElement: kAudioObjectPropertyElementMain
        )
        var propertySize = UInt32(MemoryLayout<AudioDeviceID>.size)
        let systemObjectID = AudioObjectID(kAudioObjectSystemObject)
        
        let status = AudioObjectGetPropertyData(
            systemObjectID,
            &propertyAddress,
            0,
            nil,
            &propertySize,
            &deviceID
        )
        
        if status != noErr {
            debugPrint("Error getting default output device ID: \(status)")
            return nil
        }
        
        // Get the device UID
        var deviceUID: CFString = "" as CFString
        propertyAddress.mSelector = kAudioDevicePropertyDeviceUID
        propertyAddress.mScope = kAudioObjectPropertyScopeGlobal
        propertySize = UInt32(MemoryLayout<CFString?>.size)
        
        let statusUID = AudioObjectGetPropertyData(
            deviceID,
            &propertyAddress,
            0,
            nil,
            &propertySize,
            &deviceUID
        )
        
        if statusUID != noErr {
            debugPrint("Error getting device UID: \(statusUID)")
            return nil
        }
        
        return deviceUID as String
    }
    
    func updateAudioRendererDeviceUID(_ deviceUID: String) {
        // Update the audioOutputDeviceUniqueID property
        audioRenderer.audioOutputDeviceUniqueID = deviceUID
    }
}