No audio in generated mpeg4AppleHLS by AVAssetWriter

I'm trying to use AVCaptureSession and AVAssetWriter to convert video and audio from an iPhone's camera and microphone into a fragmented video file in AppleHLS format.

Below is part of the code. It seems that the capture is successful, and I have confirmed that the data received with captureOutput() can be appended to videoWriterIput and audioWriterInput using append(). When executing audioWriterInput!.append(sampleBuffer), sampleBuffer has the following value, and it looks like the audio data has been passed to AssetWriter.

sampleBuffer.duration : CMTime(value: 941, timescale: 44100, flags: __C.CMTimeFlags(rawValue: 1), epoch: 0)
sampleBuffer.totalSampleSize : 1882

However, the final output init.mp4 and *.m4s do not contain Audio. (The video can be played without any problems.)

Could you please tell me any problems or hints as to why Audio is not included?

    /// Capture Session
    let captureSession = AVCaptureSession()
    
    /// Capture Input
    var videoDevice: AVCaptureDevice?
    var audioDevice: AVCaptureDevice?

    /// Configure and Start Capture Session
    func startCapture() {
        // Start Configuration
        captureSession.beginConfiguration()

        // Setup Input Video
        videoDevice = self.defaultCamera(cameraSide: cameraSide)
        videoDevice!.activeVideoMinFrameDuration = CMTimeMake(value: 1, timescale: 30)
        let videoInput = try AVCaptureDeviceInput(device: videoDevice!) as AVCaptureDeviceInput
        captureSession.addInput(videoInput)

        // Setup Input Audio
        audioDevice = AVCaptureDevice.default(for: AVMediaType.audio)
        let audioInput = try AVCaptureDeviceInput(device: audioDevice!) as AVCaptureDeviceInput
        captureSession.addInput(audioInput)

        // Setup Output Video
        let videoDataOutput = AVCaptureVideoDataOutput()
        videoDataOutput.setSampleBufferDelegate(self, queue: recordingQueue)
        videoDataOutput.alwaysDiscardsLateVideoFrames = true
        videoDataOutput.videoSettings = [
                kCVPixelBufferPixelFormatTypeKey: Int(kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange)] as [String : Any]
        captureSession.addOutput(videoDataOutput)

        // Setup Output Audio
        let audioDataOutput = AVCaptureAudioDataOutput()
        audioDataOutput.setSampleBufferDelegate(self, queue: recordingQueue)
        captureSession.addOutput(audioDataOutput)

        //End Configuration
        captureSession.commitConfiguration()

        // Start Capture
        captureSession.startRunning()
    }


    
    private let assetWriter: AVAssetWriter?
    private let startTimeOffset: CMTime
    private var audioWriterInput: AVAssetWriterInput?
    private let videoWriterInput: AVAssetWriterInput?

    func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {

        if assetWriter == nil {
            // AssetWriter
            assetWriter = AVAssetWriter(contentType: UTType(AVFileType.mp4.rawValue)!)
            self.startTimeOffset = CMTime(value: 1, timescale: 1)
        
            // Setup Input of Audio.
            let audioCompressionSettings: [String: Any] = [
                    AVFormatIDKey: kAudioFormatMPEG4AAC,
                    AVSampleRateKey: 44_100,
                    AVNumberOfChannelsKey: 1,
                    AVEncoderBitRateKey: 128_000
                ]
            audioWriterInput = AVAssetWriterInput(mediaType: .audio, outputSettings: audioCompressionSettings)
            audioWriterInput!.expectsMediaDataInRealTime = true
            assetWriter.add(audioWriterInput!)
        
            // Setup Input of Video.
            let videoCompressionSettings: [String: Any] = [
                    AVVideoCodecKey: AVVideoCodecType.h264
                ]

            let videoCompressionSettings: [String: Any] = [
                AVVideoCodecKey: AVVideoCodecType.h264,
                AVVideoWidthKey: 1280,
                AVVideoHeightKey: 720,
                AVVideoCompressionPropertiesKey: [
                    kVTCompressionPropertyKey_AverageBitRate: 1_024_000,
                    kVTCompressionPropertyKey_ProfileLevel: kVTProfileLevel_H264_Baseline_AutoLevel
                ]
            ]
            videoWriterInput = AVAssetWriterInput(mediaType: .video, outputSettings: videoCompressionSettings)
            videoWriterInput!.expectsMediaDataInRealTime = true
            pixelBuffer = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: videoWriterInput!, sourcePixelBufferAttributes: [kCVPixelBufferPixelFormatTypeKey as String: Int(kCVPixelFormatType_32BGRA)])
            assetWriter.add(videoWriterInput!)
              
            // Configure the asset writer for writing data in fragmented MPEG-4 format.
            assetWriter.outputFileTypeProfile = AVFileTypeProfile.mpeg4AppleHLS
            assetWriter.preferredOutputSegmentInterval = CMTime(seconds: 1.0, preferredTimescale: 1)
            assetWriter.initialSegmentStartTime = startTimeOffset
            assetWriter.delegate = self

            // start AssetWriiter
            startTime = CMSampleBufferGetPresentationTimeStamp(sampleBuffer)
            assetWriter.startWriting()
            assetWriter.startSession(atSourceTime: startTime)
        }

        let isVideo = output is AVCaptureVideoDataOutput
        if isVideo {
            if videoWriterInput.isReadyForMoreMediaData {
                videoWriterInput!.append(sampleBuffer)
            }
        }else{
            if audioWriterInput!.isReadyForMoreMediaData {
                audioWriterInput!.append(sampleBuffer)
            }
        }
    }

    func assetWriter(_ writer: AVAssetWriter, didOutputSegmentData segmentData: Data, segmentType: AVAssetSegmentType, segmentReport: AVAssetSegmentReport?) {
        :
        :
    }

No audio in generated mpeg4AppleHLS by AVAssetWriter
 
 
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