Corrupt video capturing audio and video using AVAssetWriter

问题

I am using an AVCaptureSession to use video and audio input and encode an H.264 video with AVAssetWriter.

If I don't write the audio, the video is encoded as expected. But if I write the audio, I am getting a corrupt video.

If I inspect the audio CMSampleBuffer being supplied to the AVAssetWriter it shows this information:

invalid = NO
dataReady = YES
makeDataReadyCallback = 0x0
makeDataReadyRefcon = 0x0
formatDescription = <CMAudioFormatDescription 0x17410ba30 [0x1b3a70bb8]> {
mediaType:'soun' 
mediaSubType:'lpcm' 
mediaSpecific: {
    ASBD: {
        mSampleRate: 44100.000000 
        mFormatID: 'lpcm' 
        mFormatFlags: 0xc 
        mBytesPerPacket: 2 
        mFramesPerPacket: 1 
        mBytesPerFrame: 2 
        mChannelsPerFrame: 1 
        mBitsPerChannel: 16     } 
    cookie: {(null)} 
    ACL: {(null)}
    FormatList Array: {(null)} 
} 
extensions: {(null)}

Since it is supplying lpcm audio, I have configured the AVAssetWriterInput with this setting for sound (I have tried both one and two channels):

var channelLayout = AudioChannelLayout()
memset(&channelLayout, 0, MemoryLayout<AudioChannelLayout>.size);
channelLayout.mChannelLayoutTag = kAudioChannelLayoutTag_Mono

let audioOutputSettings:[String: Any] = [AVFormatIDKey as String:UInt(kAudioFormatLinearPCM),
                                             AVNumberOfChannelsKey as String:1,
                                             AVSampleRateKey as String:44100.0,
                                            AVLinearPCMIsBigEndianKey as String:false,
                                            AVLinearPCMIsFloatKey as String:false,
                                            AVLinearPCMBitDepthKey as String:16,
                                            AVLinearPCMIsNonInterleaved as String:false,
                                             AVChannelLayoutKey: NSData(bytes:&channelLayout, length:MemoryLayout<AudioChannelLayout>.size)]

self.assetWriterAudioInput = AVAssetWriterInput(mediaType: AVMediaTypeAudio, outputSettings: audioOutputSettings)
self.assetWriter.add(self.assetWriterAudioInput)

When I use the lpcm setting above, I cannot open the video with any application. I have tried using kAudioFormatMPEG4AAC and kAudioFormatAppleLossless and I still get a corrupt video but I am able to view the video using QuickTime Player 8 (not QuickTime Player 7), but it is confused about the duration of the video and no sound is played.

When recording is complete I am calling:

func endRecording(_ completionHandler: @escaping () -> ()) {
    isRecording = false
    assetWriterVideoInput.markAsFinished()
    assetWriterAudioInput.markAsFinished()
    assetWriter.finishWriting(completionHandler: completionHandler)
}

This is how the AVCaptureSession is being configured:

func setupCapture() {

    captureSession = AVCaptureSession()

    if (captureSession == nil) {
        fatalError("ERROR: Couldnt create a capture session")
    }

    captureSession?.beginConfiguration()
    captureSession?.sessionPreset = AVCaptureSessionPreset1280x720

    let frontDevices = AVCaptureDevice.devices().filter{ ($0 as AnyObject).hasMediaType(AVMediaTypeVideo) && ($0 as AnyObject).position == AVCaptureDevicePosition.front }

    if let captureDevice = frontDevices.first as? AVCaptureDevice  {
        do {
            let videoDeviceInput: AVCaptureDeviceInput
            do {
                videoDeviceInput = try AVCaptureDeviceInput(device: captureDevice)
            }
            catch {
                fatalError("Could not create AVCaptureDeviceInput instance with error: \(error).")
            }
            guard (captureSession?.canAddInput(videoDeviceInput))! else {
                fatalError()
            }
            captureSession?.addInput(videoDeviceInput)
        }
    }

    do {
        let audioDevice = AVCaptureDevice.defaultDevice(withMediaType: AVMediaTypeAudio)
        let audioDeviceInput: AVCaptureDeviceInput
        do {
            audioDeviceInput = try AVCaptureDeviceInput(device: audioDevice)
        }
        catch {
            fatalError("Could not create AVCaptureDeviceInput instance with error: \(error).")
        }
        guard (captureSession?.canAddInput(audioDeviceInput))! else {
            fatalError()
        }
        captureSession?.addInput(audioDeviceInput)
    }

    do {
        let dataOutput = AVCaptureVideoDataOutput()
        dataOutput.videoSettings = [kCVPixelBufferPixelFormatTypeKey as String : kCVPixelFormatType_32BGRA]
        dataOutput.alwaysDiscardsLateVideoFrames = true
        let queue = DispatchQueue(label: "com.3DTOPO.videosamplequeue")
        dataOutput.setSampleBufferDelegate(self, queue: queue)
        guard (captureSession?.canAddOutput(dataOutput))! else {
            fatalError()
        }
        captureSession?.addOutput(dataOutput)

        videoConnection = dataOutput.connection(withMediaType: AVMediaTypeVideo)
    }

    do {
        let audioDataOutput = AVCaptureAudioDataOutput()
        let queue = DispatchQueue(label: "com.3DTOPO.audiosamplequeue")
        audioDataOutput.setSampleBufferDelegate(self, queue: queue)
        guard (captureSession?.canAddOutput(audioDataOutput))! else {
            fatalError()
        }
        captureSession?.addOutput(audioDataOutput)

        audioConnection = audioDataOutput.connection(withMediaType: AVMediaTypeAudio)
    }

    captureSession?.commitConfiguration()

    // this will trigger capture on its own queue
    captureSession?.startRunning()
}

The AVCaptureVideoDataOutput delegate method:

func captureOutput(_ captureOutput: AVCaptureOutput!, didOutputSampleBuffer sampleBuffer: CMSampleBuffer!, from connection: AVCaptureConnection!) {
    //  func captureOutput(captureOutput: AVCaptureOutput, sampleBuffer: CMSampleBuffer, connection:AVCaptureConnection) {

    var error: CVReturn

    if (connection == audioConnection) {
        delegate?.audioSampleUpdated(sampleBuffer: sampleBuffer)
        return
    }

    // ... Write video buffer ...//
}

Which calls:

func audioSampleUpdated(sampleBuffer: CMSampleBuffer) {
    if (isRecording) {  
        while !assetWriterAudioInput.isReadyForMoreMediaData {}
        if (!assetWriterAudioInput.append(sampleBuffer)) {
            print("Unable to write to audio input");
        }
    }
}

If I disable the assetWriterAudioInput.append() call above, then the video isn't corrupt but of course I have no audio encoded. How can I get both video and audio encoding to work?

回答1:

I figured it out. I was setting the assetWriter.startSession source time to 0, and then subtracting the start time from current CACurrentMediaTime() for writing the pixel data.

I changed the assetWriter.startSession source time to the CACurrentMediaTime() and don't subtract the current time when writing the video frame.

Old start session code:

assetWriter.startWriting()
assetWriter.startSession(atSourceTime: kCMTimeZero)

New code that works:

let presentationStartTime = CMTimeMakeWithSeconds(CACurrentMediaTime(), 240)

assetWriter.startWriting()
assetWriter.startSession(atSourceTime: presentationStartTime)

来源：https://stackoverflow.com/questions/43959376/corrupt-video-capturing-audio-and-video-using-avassetwriter