Record and Resample to aac format with AVAudioEngine, AVAudioSession setCategory AVAudioSessionCategoryRecord?

Question

I already found an example code to recording with AVAudioEngine & success to output sampleRate 22050 aac format audioFile.

After I review the code, there is a problem that I have to setCategory AVAudioSessionCategoryPlayAndRecord instead of AVAudioSessionCategoryRecord.

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

(In this case I should use "AVAudioSessionCategoryRecord", right?)

If I setCategory to AVAudioSessionCategoryRecord, I get an ERROR:

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)'

There is an example about using microphone in AVAudioSessionCategoryRecord, it seems to me that we can record only with inputNode. https://developer.apple.com/library/prerelease/content/samplecode/SpeakToMe/Introduction/Intro.html

The following is code can work now.

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()
    }
}

Record and Resample to aac format with AVAudioEngine, AVAudioSession setCategory AVAudioSessionCategoryRecord?

1 Answers1