AVAssetWriter Disrupts TCP Connection

Question

I am currently working on a project in which our application receives JPEG-data from an IP Camera through TCP (using Network -NW- framework) and builds CMSampleBuffers from it. After this process, we are displaying it with AVSampleBufferDisplayerLayer simultaneously. And if a user clicks recording button, application starts recording with AVAssetWriter.

Prior to iOS 14, we were able to record approximately 60 frames a second. But now when we start to provide CMSampleBuffers to AVAssetWriterInput; we only receive 30-40 frames per second through our TCP Connection. Somehow, starting recording with AVAssetWriter drops number of packages we receive through sockets. We don’t experience such a problem prior to iOS 14. And before/after recording, number of frame we retrieve stabilizes around 60 fps.

Any idea what may cause this?

Thanks for your help in advance!

Part we receive data through TCP:

func setupReceive(_ connection: NWConnection) {
    connection.receive(minimumIncompleteLength: 1, maximumLength: 65536) { (data, contentContext, isComplete, error) in
            if let data = data, !data.isEmpty {
                self.status = "did receive \(data.count) bytes"
                MyIPCameraManager.shared.encodeData(data)
            }
            if isComplete {
                self.stop(status: "EOF")
            } else if let error = error {
                self.connectionDidFail(error)
            } else {
                self.setupReceive(connection)
            }
        }
}

Part we initialize AVAssetWriter:

assetWriter = try? AVAssetWriter(outputURL: fileUrl, fileType: AVFileType.mp4)
        if (assetWriter == nil) {
            throw MyRecordingError.WriterInitializationError
        }
        var formatDesc: CMVideoFormatDescription? = nil
        CMVideoFormatDescriptionCreate(allocator: kCFAllocatorDefault,
                                       codecType: kCMVideoCodecType_JPEG,
                                       width: 640,
                                       height: 480,
                                       extensions: nil,
                                       formatDescriptionOut: &formatDesc)
        self.assetWriterInput = AVAssetWriterInput(mediaType: AVMediaType.video, outputSettings: nil, sourceFormatHint: formatDesc)
        self.assetWriterInput.expectsMediaDataInRealTime = true
        self.assetWriter.add(assetWriterInput)