使用AVAudioEngine，AVAudioSession setCategory AVAudioSessionCategoryRecord记录并重新采样aac格式？

我已经找到了一个示例代码来录制AVAudioEngine &成功输出sampleRate 22050 aac格式的audioFile。使用AVAudioEngine，AVAudioSession setCategory AVAudioSessionCategoryRecord记录并重新采样aac格式？

我查看了代码后，出现了一个问题，我必须设置类AVAudioSessionCategoryPlayAndRecord而不是AVAudioSessionCategoryRecord。

How to improve the code for using "AVAudioSessionCategoryRecord" without "PlayAndRecord"?

（在这种情况下，我应该使用 “AVAudioSessionCategoryRecord” 吧？）

如果我setCategory到AVAudioSessionCategoryRecord，我得到一个错误：

AVAudioEngineGraph.mm:1070: Initialize: required condition is false: IsFormatSampleRateAndChannelCountValid(outputHWFormat)

Terminating app due to uncaught exception 'com.apple.coreaudio.avfaudio', reason: 'required condition is false: IsFormatSampleRateAndChannelCountValid(outputHWFormat)'

有一个关于使用麦克风的例子在AVAudioSessionCategoryRecord中，在我看来，我们只能用inputNode记录。 https://developer.apple.com/library/prerelease/content/samplecode/SpeakToMe/Introduction/Intro.html

以下代码现在可以工作。

import UIKit 
import AVFoundation 

class ViewController: UIViewController { 

    let audioEngine = AVAudioEngine() 
    lazy var inputNode : AVAudioInputNode = { 
     return self.audioEngine.inputNode! 
    }() 

    let sampleRate = Double(22050) 
    lazy var outputFormat : AVAudioFormat = { 
     return AVAudioFormat(commonFormat: self.inputNode.outputFormatForBus(0).commonFormat, 
          sampleRate: self.sampleRate, 
          channels: AVAudioChannelCount(1), 
          interleaved: false) 
    }() 

    let converterNode = AVAudioMixerNode() 
    lazy var aacFileURL : NSURL = { 
     let dirPath = NSURL(fileURLWithPath: NSTemporaryDirectory(), isDirectory: true) 
     let filePath = dirPath.URLByAppendingPathComponent("rec.aac") 
     return filePath 
    }() 

    lazy var outputAACFile : AVAudioFile = { 
     var settings = self.outputFormat.settings 
     settings[AVFormatIDKey] = NSNumber(unsignedInt: kAudioFormatMPEG4AAC) 
     return try! AVAudioFile(forWriting: self.aacFileURL, 
           settings:settings) 
    }() 

    override func viewDidAppear(animated: Bool) { 
     super.viewDidAppear(animated) 

     let audioSession = AVAudioSession.sharedInstance() 
     try! audioSession.setCategory(AVAudioSessionCategoryPlayAndRecord) 
     try! audioSession.setActive(true) 

     self.audioEngine.attachNode(converterNode) 
     self.audioEngine.connect(inputNode, 
           to: converterNode, 
           format: inputNode.outputFormatForBus(0)) 

     self.audioEngine.connect(converterNode, 
           to: self.audioEngine.mainMixerNode, 
           format: outputFormat) 

     converterNode.volume = 0 

     converterNode.installTapOnBus(0, bufferSize: 1024, format: converterNode.outputFormatForBus(0)) { (buffer, when) in 

      try! self.outputAACFile.writeFromBuffer(buffer) 
     } 

     try! self.audioEngine.start() 
    } 
}

关联链接

How can I specify the format of AVAudioEngine Mic-Input?

Recording audio file using AVAudioEngine

来源

2016-07-29 w91379137