与 ScreenCaptureKit 一起使用的 AVAssetWriter 会导致文件损坏和错误

Question

我正在尝试使用 ScreenCaptureKit 编写一个可以记录会议的应用程序。 但是，每当我实例化一个 AVAssetWriter 并开始将CMSampleBuffers流式传输到它时，它都会因错误而失败

Optional(Error Domain=AVFoundationErrorDomain Code=-11800 \"The operation could not be completed\" UserInfo={NSLocalizedFailureReason=An unknown error occurred (-12785), NSLocalizedDescription=The operation could not be completed, NSUnderlyingError=0x600000c066d0 {Error Domain=NSOSStatusErrorDomain Code=-12785 \"(null)\"}})

我在这个 repo 有一个完整的代码复制 - https://github.com/jonluca/buggy-avassetwriter

奇怪的是，这个 repo 有效，其中约 95% 是相同的代码https://github.com/garethpaul/ScreenRecorderMacOS

我可能只是不适应 AVAssetWriter 和更新的 ScreenCaptureKit 的复杂性，但我不确定这个错误是如何发生的。

Answer 1

好吧，这花了一段时间才弄清楚，但事实证明，您不能只检查CMSampleBuffer是否有效。 看起来它仍然可能无效，所以我添加了一个名为isValidFrame的实用程序来检查 SCFrameStatus 选项以及其他一些键

    private func isValidFrame(for sampleBuffer: CMSampleBuffer) -> Bool {

        // Retrieve the array of metadata attachments from the sample buffer.
        guard let attachmentsArray = CMSampleBufferGetSampleAttachmentsArray(sampleBuffer,
                                                                             createIfNecessary: false) as? [[SCStreamFrameInfo: Any]],
              let attachments = attachmentsArray.first
        else {
            return false
        }

        // Validate the status of the frame. If it isn't `.complete`, return nil.
        guard let statusRawValue = attachments[SCStreamFrameInfo.status] as? Int,
              let status = SCFrameStatus(rawValue: statusRawValue),
              status == .complete
        else {
            return false
        }

        // Get the pixel buffer that contains the image data.
        guard let pixelBuffer = sampleBuffer.imageBuffer else {
            return false
        }

        // Get the backing IOSurface.
        guard let surfaceRef = CVPixelBufferGetIOSurface(pixelBuffer)?.takeUnretainedValue() else {
            return false
        }
        let surface = unsafeBitCast(surfaceRef, to: IOSurface.self)

        // Retrieve the content rectangle, scale, and scale factor.
        guard let contentRectDict = attachments[.contentRect],
              let contentRect = CGRect(dictionaryRepresentation: contentRectDict as! CFDictionary),
              let contentScale = attachments[.contentScale] as? CGFloat,
              let scaleFactor = attachments[.scaleFactor] as? CGFloat
        else {
            return false
        }

        return true
    }

    /// - Tag: DidOutputSampleBuffer
    func stream(_ stream: SCStream,
                didOutputSampleBuffer sampleBuffer: CMSampleBuffer,
                of outputType: SCStreamOutputType) {
        // Return early if the sample buffer is invalid.
        guard sampleBuffer.isValid else {
            return
        }

        // Determine which type of data the sample buffer contains.
        switch outputType {
        case .audio:
            self.recordComputerAudio(sampleBuffer: sampleBuffer)
        case .screen:
            guard isValidFrame(for: sampleBuffer) else {
                return
            }
            self.recordFrame(sampleBuffer: sampleBuffer)
        @unknown default:
            fatalError("Encountered unknown stream output type: \(outputType)")
        }
    }