Apple's sample code "AVReaderWriter: Offline Audio / Video Processing" has the following listing let writingGroup = dispatch_group_create() // Transfer data from input file to output file. self.transferVideoTracks(videoReaderOutputsAndWriterInputs, group: writingGroup) self.transferPassthroughTracks(passthroughReaderOutputsAndWriterInputs, group: writingGroup) // Handle completion. let queue = dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0) dispatch_group_notify(writingGroup, queue) { // `readingAndWritingDidFinish()` is guaranteed to call `finish()` exactly once. self.readingAndWritingDidFinish(assetReader, assetWriter: assetWriter) } in CynanifyOperation.swift (an NSOperation subclass that stylizes imported video and exports it). How would I get about writing this part in modern Swift so that it compiles and works? I've tried writing this as let writingGroup = DispatchGroup() // Transfer data from input file to output file. self.transferVideoTracks(videoReaderOutputsAndWriterInputs: videoReaderOutputsAndWriterInputs, group: writingGroup) self.transferPassthroughTracks(passthroughReaderOutputsAndWriterInputs: passthroughReaderOutputsAndWriterInputs, group: writingGroup) // Handle completion. writingGroup.notify(queue: .global()) { // `readingAndWritingDidFinish()` is guaranteed to call `finish()` exactly once. self.readingAndWritingDidFinish(assetReader: assetReader, assetWriter: assetWriter) } However, it's taking an extremely long time for self.readingAndWritingDidFinish(assetReader: assetReader, assetWriter: assetWriter) to be called, and my UI is stuck in the ProgressViewController with a loading spinner. Is there something I wrote incorrectly or missed conceptually in the Swift 5 version?

Apple's sample code Identifying Trajectories in Video contains the following delegate callback: func cameraViewController(_ controller: CameraViewController, didReceiveBuffer buffer: CMSampleBuffer, orientation: CGImagePropertyOrientation) { let visionHandler = VNImageRequestHandler(cmSampleBuffer: buffer, orientation: orientation, options: [:]) if gameManager.stateMachine.currentState is GameManager.TrackThrowsState { DispatchQueue.main.async { // Get the frame of rendered view let normalizedFrame = CGRect(x: 0, y: 0, width: 1, height: 1) self.jointSegmentView.frame = controller.viewRectForVisionRect(normalizedFrame) self.trajectoryView.frame = controller.viewRectForVisionRect(normalizedFrame) } // Perform the trajectory request in a separate dispatch queue. trajectoryQueue.async { do { try visionHandler.perform([self.detectTrajectoryRequest]) if let results = self.detectTrajectoryRequest.results { DispatchQueue.main.async { self.processTrajectoryObservations(controller, results) } } } catch { AppError.display(error, inViewController: self) } } } } However, instead of drawing UI whenever detectTrajectoryRequest.results exist (https://developer.apple.com/documentation/vision/vndetecttrajectoriesrequest/3675672-results), I'm interested in using the CMTimeRange provided by each result to construct a new video. In effect, this would filter down the original video to only frames with trajectories. How might I accomplish this, perhaps through writing only specific time ranges' frames from one AVFoundation video to a new AVFoundation video?

I'd like a user's upload operation that's started in the foreground to continue when they leave the app. Apple's article Extending Your App's Background Execution Time has the following code listing func sendDataToServer( data : NSData ) { // Perform the task on a background queue. DispatchQueue.global().async { // Request the task assertion and save the ID. self.backgroundTaskID = UIApplication.shared. beginBackgroundTask (withName: "Finish Network Tasks") { // End the task if time expires. UIApplication.shared.endBackgroundTask(self.backgroundTaskID!) self.backgroundTaskID = UIBackgroundTaskInvalid } // Send the data synchronously. self.sendAppDataToServer( data: data) // End the task assertion. UIApplication.shared.endBackgroundTask(self.backgroundTaskID!) self.backgroundTaskID = UIBackgroundTaskInvalid } } The call to self.sendAppDataToServer( data: data) is unclear. Is this where the upload operation would go, wrapped in Dispatch.global().sync { }?