AVMultiCamPiP: Capturing from Multiple Cameras

At a glance

Project structure

Source bundle/
├── AVMultiCamPiP/
│   ├── AppDelegate.swift
│   ├── CameraViewController.swift
│   ├── MovieRecorder.swift
│   ├── PreviewView.swift
│   ├── PiPVideoMixer.swift
│   ├── PiPMixer.metal
│   ├── Utilities.swift
│   ├── Base.lproj/
│   │   ├── LaunchScreen.storyboard
│   │   └── Main.storyboard
│   └── Info.plist
└── AVMultiCamPiP.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: Metal, Swift.
• The verified tree contains 6 project/configuration file(s) and 9 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["ViewController"]
    N3["MovieRecorder"]
    N4["AVFoundation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

AVMultiCamPiP/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
}

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 AVFoundation.

Ownership and state

classDiagram
    AppDelegate o-- UIWindow : window
    ViewController o-- Issessionrunning : isSessionRunning
    ViewController o-- Setupresult : setupResult
    ViewController o-- Renderingenabled : renderingEnabled

Ownership evidence

AVMultiCamPiP/AppDelegate.swift:12 — stored dependency or nearest verified ownership anchor

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
}

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

AVMultiCamPiP/CameraViewController.swift:69 — representative execution boundary

                DispatchQueue.main.async {
                    let changePrivacySetting = "\(Bundle.main.applicationName) doesn't have permission to use the camera, please change privacy settings"
                    let message = NSLocalizedString(changePrivacySetting, comment: "Alert message when the user has denied access to the camera")
                    // ...
                }

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

AVMultiCamPiP/AppDelegate.swift:11 — representative type boundary

@UIApplicationMain
class AppDelegate: UIResponder, UIApplicationDelegate {
    var window: UIWindow?
}

No local protocol conformance is claimed as protocol-oriented design; external framework conformances are listed only as dependencies.

Access control

Reference code

AVMultiCamPiP/CameraViewController.swift:129 — representative boundary

    @objc // Expose to Objective-C for use with #selector()
    private func didEnterBackground(notification: NSNotification) {
        // ...
            self.renderingEnabled = false
        // ...
    }

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: ViewController; Delegate: AppDelegate; Recorder: MovieRecorder; View: PreviewView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: viewDidLoad, viewWillAppear, viewWillDisappear, didEnterBackground, willEnterForground, addObservers, removeObservers, togglePiP.
• Files: AVMultiCamPiP/AppDelegate.swift, AVMultiCamPiP/MovieRecorder.swift, AVMultiCamPiP/PreviewView.swift, AVMultiCamPiP/PiPVideoMixer.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches AVFoundation, UIKit, CoreMedia, CoreVideo 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.
• The source does not justify labeling the design protocol-oriented.

Source map

• Official Apple documentation