Detecting moving objects in a video

At a glance

Project structure

Source bundle/
├── VisionTrajectoryDemo/
│   ├── AppDelegate.swift
│   ├── CameraViewController.swift
│   ├── Custom Views/
│   │   ├── VideoRenderView.swift
│   │   └── CameraFeedView.swift
│   ├── ContentAnalysisViewController.swift
│   ├── HomeViewController.swift
│   ├── SceneDelegate.swift
│   ├── SpriteKit Views/
│   │   ├── BallScene.swift
│   │   ├── TrajectoryView.swift
│   │   └── Animations.swift
│   └── AppError.swift
└── Configuration/
    └── SampleCode.xcconfig

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Swift.
• The verified tree contains 7 project/configuration file(s) and 14 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["CameraViewController"]
    N3["Vision APIs"]
    N1 --> N2
    N2 --> N3

Reference code

VisionTrajectoryDemo/AppDelegate.swift:10 — architecture anchor

@main
class AppDelegate: UIResponder, UIApplicationDelegate {
    // ...
    func application(_ application: UIApplication,
                     didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        return true
    }
    // ...
}

Interpretation

The arrows summarize the source-visible entry, role-named types or folders, and framework direction; when nodes come from structural folders, the sequence is a high-level interpretation rather than proof that every adjacent node calls the next. Ownership is claimed only where the next section cites a stored property or assignment. The diagram is intentionally limited to the dominant path into Vision.

Ownership and state

classDiagram
    VideoRenderView o-- CALayer : renderLayer
    ContentAnalysisViewController o-- UIButton : closeButton
    ContentAnalysisViewController o-- AVAsset : recordedVideoSource
    ContentAnalysisViewController o-- CameraViewController : cameraViewController

Ownership evidence

VisionTrajectoryDemo/Custom Views/VideoRenderView.swift:18 — stored dependency or nearest verified ownership anchor

class VideoRenderView: UIView, NormalizedRectConverting {
    // ...
    private var renderLayer: CALayer!
    // ...
}

Composition arrows indicate a source-visible construction expression or locally owned value state; aggregation means the owner stores or receives a dependency without proving exclusive lifetime ownership.

Concurrency, scheduling, and thread safety

Evidence limit: actor isolation, async/await, or Task creation does not by itself prove background-thread execution; Sendable conformance alone does not prove thread-safe mutation.

@MainActor/MainActor.run, DispatchQueue.main, and RunLoop.main are reported as distinct isolation, queue, and event-loop mechanisms. A plain Task is kept separate from Task.detached; neither is labeled as a background thread.

Reference code

VisionTrajectoryDemo/CameraViewController.swift:23 — representative execution boundary

class CameraViewController: UIViewController {
    // ...
    private let videoDataOutputQueue = DispatchQueue(label: "CameraFeedDataOutput",
                                                     qos: .userInitiated,
                                                     attributes: [],
                                                     autoreleaseFrequency: .workItem)
    // ...
}

State propagation, frameworks, and dependencies

Evidence limit: an import proves a source-level compilation dependency at the cited line; it does not prove runtime use, architectural adoption, or whether a Swift package is a direct application dependency.

receive(on:) describes downstream delivery scheduling, while subscribe(on:) describes upstream subscription/request/cancel scheduling. An import Combine alone establishes neither behavior nor a Store, reducer, Redux, or other application architecture.

Class and protocol design

VisionTrajectoryDemo/CameraViewController.swift:11 — representative type boundary

protocol CameraViewControllerOutputDelegate: AnyObject {
    func cameraViewController(_ controller: CameraViewController,
                              didReceiveBuffer buffer: CMSampleBuffer,
                              orientation: CGImagePropertyOrientation)
}

The source explicitly defines local protocol relationships: CameraFeedView → NormalizedRectConverting, VideoRenderView → NormalizedRectConverting, TrajectoryView → AnimatedTransitioning, ContentAnalysisViewController → CameraViewControllerOutputDelegate.

Access control

Reference code

VisionTrajectoryDemo/CameraViewController.swift:23 — representative boundary

class CameraViewController: UIViewController {
    // ...
    private let videoDataOutputQueue = DispatchQueue(label: "CameraFeedDataOutput",
                                                     qos: .userInitiated,
                                                     attributes: [],
                                                     autoreleaseFrequency: .workItem)
    // ...
}

Swift declarations without a modifier are internal; explicit private, fileprivate, private(set), public, or open entries above are interpreted by language semantics. Objective-C/C samples instead rely on header and implementation boundaries, which are not equivalent to Swift lexical privacy.

Logic ownership and placement

Design patterns

Naming conventions

• Types: Controller: CameraViewController, ContentAnalysisViewController, HomeViewController; Delegate: AppDelegate, CameraViewControllerOutputDelegate, SceneDelegate; Scene: BallScene; View: CameraFeedView, TrajectoryView, VideoRenderView.
• Protocols: CameraViewControllerOutputDelegate, NormalizedRectConverting, AnimatedTransitioning.
• Methods: application, cameraViewController, viewDidDisappear, setupAVSession, viewRectForVisionRect, setupVideoOutputView, startReadingAsset, captureOutput.
• Files: VisionTrajectoryDemo/AppDelegate.swift, VisionTrajectoryDemo/CameraViewController.swift, VisionTrajectoryDemo/Custom Views/VideoRenderView.swift, VisionTrajectoryDemo/ContentAnalysisViewController.swift, VisionTrajectoryDemo/Custom Views/CameraFeedView.swift, VisionTrajectoryDemo/HomeViewController.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, AVFoundation, SpriteKit, Vision through a deliberately small high-level chain; the detailed API graph remains inside the cited implementation files.
• Stored-property evidence identifies lifecycle collaboration; it does not by itself prove exclusive object ownership.
• Access-control conclusions separate verified language visibility from the likely design rationale.
• Local protocol relationships provide an explicit substitution boundary.

Source map

• Official Apple documentation