As far as I can tell - https://developer.apple.com/documentation/vision/identifying_trajectories_in_video trajectory detection lets you use characteristics of the trajectories detected for, say, drawing over the video as it plays. However, is it possible to mark which time ranges the video has detected trajectories, or perhaps access the frames for which there are trajectories?

I'd like to perform VNDetectHumanBodyPoseRequests on a video that the user imports through the system photo picker or document view controller. I started looking at the Building a Feature-Rich App for Sports Analysis - https://developer.apple.com/documentation/vision/building_a_feature-rich_app_for_sports_analysis sample code since it has an example where video is imported from disk and then analyzed. However, my end goal is to filter for frames that contain certain poses, so that all frames without them are edited out / deleted (instead of in the sample code drawing on frames with detected trajectories). For pose detection I'm looking at the Detecting Human Actions in a Live Video Feed - https://developer.apple.com/documentation/createml/detecting_human_actions_in_a_live_video_feed, but the live video capture isn't quite relevant. I'm trying to break this down into smaller problems and have a few questions: Should a full video file copy be made before analysis? The Detecting Human Actions in a Live Video Feed - https://developer.apple.com/documentation/createml/detecting_human_actions_in_a_live_video_feed sample code uses a Combine pipeline for analyzing live video frames. Since I'm analyzing imported video, would Combine be overkill or a good fit here? After I've detected which frames have a particular pose, how (in AVFoundation terms) do I filter for those frames or edit out / delete the frames without that pose?

I've been looking through Apple's sample code Building a Feature-Rich App for Sports Analysis - https://developer.apple.com/documentation/vision/building_a_feature-rich_app_for_sports_analysis and its associated WWDC video to learn to reason about AVFoundation and VNDetectTrajectoriesRequest - https://developer.apple.com/documentation/vision/vndetecttrajectoriesrequest. My goal is to allow the user to import videos (this part I have working, the user sees a UIDocumentBrowserViewController - https://developer.apple.com/documentation/uikit/uidocumentbrowserviewcontroller, picks a video file, and then a copy is made), but I only want segments of the original video copied where trajectories are detected from a ball moving. I've tried as best I can to grasp the two parts, at the very least finding where the video copy is made and where the trajectory request is made. The full video copy happens in CameraViewController.swift (I'm starting with just imported video for now and not reading live from the device's video camera), line 160:func startReadingAsset(_ asset: AVAsset) { videoRenderView = VideoRenderView(frame: view.bounds) setupVideoOutputView(videoRenderView) let displayLink = CADisplayLink(target: self, selector: #selector(handleDisplayLink(:))) displayLink.preferredFramesPerSecond = 0 displayLink.isPaused = true displayLink.add(to: RunLoop.current, forMode: .default) guard let track = asset.tracks(withMediaType: .video).first else { AppError.display(AppError.videoReadingError(reason: "No video tracks found in AVAsset."), inViewController: self) return } let playerItem = AVPlayerItem(asset: asset) let player = AVPlayer(playerItem: playerItem) let settings = [ String(kCVPixelBufferPixelFormatTypeKey): kCVPixelFormatType420YpCbCr8BiPlanarFullRange ] let output = AVPlayerItemVideoOutput(pixelBufferAttributes: settings) playerItem.add(output) player.actionAtItemEnd = .pause player.play() self.displayLink = displayLink self.playerItemOutput = output self.videoRenderView.player = player let affineTransform = track.preferredTransform.inverted() let angleInDegrees = atan2(affineTransform.b, affineTransform.a) * CGFloat(180) / CGFloat.pi var orientation: UInt32 = 1 switch angleInDegrees { case 0: orientation = 1 // Recording button is on the right case 180, -180: orientation = 3 // abs(180) degree rotation recording button is on the right case 90: orientation = 8 // 90 degree CW rotation recording button is on the top case -90: orientation = 6 // 90 degree CCW rotation recording button is on the bottom default: orientation = 1 } videoFileBufferOrientation = CGImagePropertyOrientation(rawValue: orientation)! videoFileFrameDuration = track.minFrameDuration displayLink.isPaused = false } @objc private func handleDisplayLink(_ displayLink: CADisplayLink) { guard let output = playerItemOutput else { return } videoFileReadingQueue.async { let nextTimeStamp = displayLink.timestamp + displayLink.duration let itemTime = output.itemTime(forHostTime: nextTimeStamp) guard output.hasNewPixelBuffer(forItemTime: itemTime) else { return } guard let pixelBuffer = output.copyPixelBuffer(forItemTime: itemTime, itemTimeForDisplay: nil) else { return } // Create sample buffer from pixel buffer var sampleBuffer: CMSampleBuffer? var formatDescription: CMVideoFormatDescription? CMVideoFormatDescriptionCreateForImageBuffer(allocator: nil, imageBuffer: pixelBuffer, formatDescriptionOut: &formatDescription) let duration = self.videoFileFrameDuration var timingInfo = CMSampleTimingInfo(duration: duration, presentationTimeStamp: itemTime, decodeTimeStamp: itemTime) CMSampleBufferCreateForImageBuffer(allocator: nil, imageBuffer: pixelBuffer, dataReady: true, makeDataReadyCallback: nil, refcon: nil, formatDescription: formatDescription!, sampleTiming: &timingInfo, sampleBufferOut: &sampleBuffer) if let sampleBuffer = sampleBuffer { self.outputDelegate?.cameraViewController(self, didReceiveBuffer: sampleBuffer, orientation: self.videoFileBufferOrientation) DispatchQueue.main.async { let stateMachine = self.gameManager.stateMachine if stateMachine.currentState is GameManager.SetupCameraState { // Once we received first buffer we are ready to proceed to the next state stateMachine.enter(GameManager.DetectingBoardState.self) } } } } } Line 139 self.outputDelegate?.cameraViewController(self, didReceiveBuffer: sampleBuffer, orientation: self.videoFileBufferOrientation) is where the video sample buffer is passed to the Vision framework subsystem for analyzing trajectories, the second part. This delegate callback is implemented in GameViewController.swift on line 335: // 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) } } Trajectories found are drawn over the video in self.processTrajectoryObservations(controller, results). Where I'm stuck now is modifying this so that instead of drawing the trajectories, the new video only copies parts of the original video to it where trajectories were detected in the frame.

A quick web search shows that storing them in a plist is not recommended. What are the best practices here?

"Code signing 'WatchDeuce Extension.appex' failed." "View distribution logs for more information." Does anyone have any suggestions for a solution or workaround? I've filed this as FB9171462 with the logs attached.

For example, Operation A both fetches model data over the network and updates a UICollectionViewbacked by it. Operation B filters model data. What is a good approach to executing B only after A is finished?

When synchronizing model objects, local CKRecords, and CKRecords in CloudKit during swipe-to-delete, how can I make this as robust as possible? Error handling omitted for the sake of the example. override func tableView(_ tableView: UITableView, commit editingStyle: UITableViewCell.EditingStyle, forRowAt indexPath: IndexPath) {         if editingStyle == .delete {             let record = self.records[indexPath.row]             privateDatabase.delete(withRecordID: record.recordID) { recordID, error in                 self.records.remove(at: indexPath.row)             }         }     } Since indexPath could change due to other changes in the table view / collection view during the time it takes to delete the record from CloudKit, how could this be improved upon?

Is there a UIKit equivalent to SwiftUI's confirmationDialog(_:isPresented:titleVisibility:actions:)?

How do you create a picker where the user's selection corresponds to different values of an enumerated type?

I have an app that currently depends on fetching the model through CloudKit, and is composed of value types. I'm considering adding Core Data support so that record modifications are robust regardless of network conditions. Core Data resources seem to always assume a model layer with reference semantics, so I'm not sure where to begin. Should I keep my top-level model type a struct? Can I? If I move my model to reference semantics, how might I bridge from past model instances that are fetched through CloudKit and then decoded? Thank you in advance.

I observe when an AVPlayer finishes play in order to present a UIAlert at the end time. NotificationCenter.default.addObserver( self, selector: #selector(presentAlert), name: .AVPlayerItemDidPlayToEndTime, object: nil ) I've had multiple user reports of the alert happening where they're not intended, such as the middle of the video after replaying, and on other views. I'm unable to reproduce this myself, but my guess is that it's a threading issue since AVPlayerItemDidPlayToEndTime says "the system may post this notification on a thread other than the one used to registered the observer." How then do I make sure the alert is present on the main thread? Should I dispatch to the main queue from within my presentAlert function, or add the above observer with addObserver(forName:object:queue:using:) instead, passing in the main operation queue?

The Swift book says that "to prevent strong reference cycles, delegates are declared as weak references." protocol SomeDelegate: AnyObject { } class viewController: UIViewController, SomeDelegate { weak var delegate: SomeDelegate? override func viewDidLoad() { delegate = self } } Say the class parameterizes a struct with that delegate class viewController: UIViewController, SomeDelegate { weak var delegate: SomeDelegate? override func viewDidLoad() { delegate = self let exampleView = ExampleView(delegate: delegate) let hostingController = UIHostingController(rootView: exampleView) self.present(hostingController, animated: true) } } struct ExampleView: View { var delegate: SomeDelegate! var body: some View { Text("") } } Should the delegate property in the struct also be marked with weak?

How do I resolve this issue when trying to re-import a custom SF Symbol into Apple's SF Symbols app? Is there an exact export configuration I'm missing in Sketch or Figma?

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 { }?

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?