删除 AVAssetWriter 第一个黑色/空白帧

我有一个avassetwriter使用应用的过滤器录制视频，然后通过avqueueplayer.

我的问题是，在播放时，录制的视频在第一帧显示黑屏/空白屏幕。据我了解，这是由于作者在捕获第一个实际视频帧之前捕获了音频。

为了尝试解决这个问题，我在附加到音频编写器输入时进行了布尔检查，以确定第一个视频帧是否已附加到适配器。也就是说，尽管已经打印了时间戳，但我仍然在播放时看到黑框，这表明视频先于音频...我还尝试在输出==视频时进行检查以启动写入会话，但最终得到了相同的结果。

任何指导或其他解决方法将不胜感激。

func captureOutput(_ output: AVCaptureOutput, didOutput sampleBuffer: CMSampleBuffer, from connection: AVCaptureConnection) {
        
let timestamp = CMSampleBufferGetPresentationTimeStamp(sampleBuffer).seconds

if output == _videoOutput {
    if connection.isVideoOrientationSupported { connection.videoOrientation = .portrait }
        
    guard let cvImageBuffer = CMSampleBufferGetImageBuffer(sampleBuffer) else { return }
    let ciImage = CIImage(cvImageBuffer: cvImageBuffer)

    guard let filteredCIImage = applyFilters(inputImage: ciImage) else { return }
    self.ciImage = filteredCIImage

    guard let cvPixelBuffer = getCVPixelBuffer(from: filteredCIImage) else { return }
    self.cvPixelBuffer = cvPixelBuffer
        
    self.ciContext.render(filteredCIImage, to: cvPixelBuffer, bounds: filteredCIImage.extent, colorSpace: CGColorSpaceCreateDeviceRGB())
        
    metalView.draw()
}
        
switch _captureState {
case .start:
    
    guard let outputUrl = tempURL else { return }
    
    let writer = try! AVAssetWriter(outputURL: outputUrl, fileType: .mp4)
    
    let videoSettings = _videoOutput!.recommendedVideoSettingsForAssetWriter(writingTo: .mp4)
    let videoInput = AVAssetWriterInput(mediaType: .video, outputSettings: videoSettings)
    videoInput.mediaTimeScale = CMTimeScale(bitPattern: 600)
    videoInput.expectsMediaDataInRealTime = true
    
    let pixelBufferAttributes = [
        kCVPixelBufferCGImageCompatibilityKey: NSNumber(value: true),
        kCVPixelBufferCGBitmapContextCompatibilityKey: NSNumber(value: true),
        kCVPixelBufferPixelFormatTypeKey: NSNumber(value: Int32(kCVPixelFormatType_32ARGB))
    ] as [String:Any]
    
    let adapter = AVAssetWriterInputPixelBufferAdaptor(assetWriterInput: videoInput, sourcePixelBufferAttributes: pixelBufferAttributes)
    if writer.canAdd(videoInput) { writer.add(videoInput) }
                            
    let audioSettings = _audioOutput!.recommendedAudioSettingsForAssetWriter(writingTo: .mp4) as? [String:Any]
    let audioInput = AVAssetWriterInput(mediaType: .audio, outputSettings: audioSettings)
    audioInput.expectsMediaDataInRealTime = true
    if writer.canAdd(audioInput) { writer.add(audioInput) }

    _filename = outputUrl.absoluteString
    _assetWriter = writer
    _assetWriterVideoInput = videoInput
    _assetWriterAudioInput = audioInput
    _adapter = adapter
    _captureState = .capturing
    _time = timestamp
                
    writer.startWriting()
    writer.startSession(atSourceTime: CMTime(seconds: timestamp, preferredTimescale: CMTimeScale(600)))
    
case .capturing:
    
    if output == _videoOutput {
        if _assetWriterVideoInput?.isReadyForMoreMediaData == true {
            let time = CMTime(seconds: timestamp, preferredTimescale: CMTimeScale(600))
            _adapter?.append(self.cvPixelBuffer, withPresentationTime: time)

            if !hasWrittenFirstVideoFrame { hasWrittenFirstVideoFrame = true }
        }
    } else if output == _audioOutput {
        if _assetWriterAudioInput?.isReadyForMoreMediaData == true, hasWrittenFirstVideoFrame {
            _assetWriterAudioInput?.append(sampleBuffer)
        }
    }
    break
    
case .end:
    
    guard _assetWriterVideoInput?.isReadyForMoreMediaData == true, _assetWriter!.status != .failed else { break }
    
    _assetWriterVideoInput?.markAsFinished()
    _assetWriterAudioInput?.markAsFinished()
    _assetWriter?.finishWriting { [weak self] in
        
        guard let output = self?._assetWriter?.outputURL else { return }
        
        self?._captureState = .idle
        self?._assetWriter = nil
        self?._assetWriterVideoInput = nil
        self?._assetWriterAudioInput = nil
        
        
        self?.previewRecordedVideo(with: output)
    }
    
default:
    break
}
}

确实，在.capturing声明您通过丢弃前面的音频样本缓冲区来确保写入的第一个样本缓冲区是视频样本缓冲区 -however您仍然允许音频样本缓冲区的呈现时间戳来启动时间线writer.startSession(atSourceTime:)。这意味着您的视频开始什么也没有，因此您不仅短暂地听不到任何声音（很难注意到），而且也看不到任何声音，您的视频播放器恰好用黑框表示。

从这个角度来看，有没有要删除的黑框，只有一个空白需要填补。您可以通过从第一个视频时间戳开始会话来填补此空白。

这可以通过防止非视频样本缓冲区来实现.start状态，或者通过移动不太干净writer.startSession(atSourceTime:) into if !hasWrittenFirstVideoFrame {}我猜。

附注为什么你要在之间来回转换CMTime和秒？为什么不坚持CMTime?