AVAudioEngine低音量

Question

我正在用Swift编写一个iOS应用程序，它记录用户的语音，然后可以用一些语音效果回放它，但问题是，当使用内置iPhone麦克风时，回放非常安静。使用耳机是没有问题的。

录制代码：

let recordingName = "my_audio.m4a"
let pathArray = [dirPath, recordingName]
let filePath = NSURL.fileURLWithPathComponents(pathArray)
print(filePath)

let recordSettings: [String: AnyObject] = [
    AVFormatIDKey: Int(kAudioFormatAppleLossless),
    AVEncoderAudioQualityKey : AVAudioQuality.Max.rawValue,
    AVEncoderBitRateKey : 320000,
    AVNumberOfChannelsKey: 2,
    AVSampleRateKey : 44100.0
]

let session = AVAudioSession.sharedInstance()
try! session.setCategory(AVAudioSessionCategoryPlayAndRecord)
try! audioRecorder = AVAudioRecorder(URL: filePath!, settings: recordSettings)

audioRecorder.meteringEnabled = true
audioRecorder.updateMeters()
audioRecorder.delegate = self
audioRecorder.prepareToRecord()
audioRecorder.record()

播放代码：

playerNode.stop()
playerNode.volume = 1.0
audioEngine.stop()
audioEngine.reset()

audioEngine.attachNode(playerNode)
audioEngine.attachNode(audioUnitTime)
audioEngine.connect(playerNode, to: audioUnitTime, format: receivedAudio.processingFormat)
audioEngine.connect(audioUnitTime, to: audioEngine.outputNode, format: receivedAudio.processingFormat)

playerNode.scheduleFile(receivedAudio, atTime: nil, completionHandler: nil)
try! audioEngine.start()
playerNode.play()

对我来说，唯一的解决方案是，最初的苹果语音记录应用程序也会做同样的事情，但只有在右上角的扬声器图标被禁用的情况下才会这样做。尽管我没能找到那个扬声器图标是做什么用的。

Answer 1

好了，我终于找到了。问题出在AVAudioSession上：

let session = AVAudioSession.sharedInstance()
try! session.setCategory(AVAudioSessionCategoryPlayAndRecord, withOptions:AVAudioSessionCategoryOptions.DefaultToSpeaker)