Capturing screen content in macOS

At a glance

Project structure

Source bundle/
├── CaptureSample/
│   ├── CaptureSampleApp.swift
│   ├── ScreenRecorder.swift
│   ├── Views/
│   │   ├── ConfigurationView.swift
│   │   ├── PickerSettingsView.swift
│   │   ├── AudioLevelsView.swift
│   │   ├── MaterialView.swift
│   │   └── CapturePreview.swift
│   ├── CaptureEngine.swift
│   ├── ContentView.swift
│   ├── PowerMeter.swift
│   └── AudioPlayer.swift
└── CaptureSample.xcodeproj/
    └── .xcodesamplecode.plist

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 4 project/configuration file(s) and 24 source declaration(s).

Overall architecture

flowchart LR
    N1["CaptureSampleApp"]
    N2["ContentView"]
    N3["AudioLevelProvider"]
    N4["ScreenCaptureKit APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

CaptureSample/CaptureSampleApp.swift:9 — architecture anchor

@main
struct CaptureSampleApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .frame(minWidth: 960, minHeight: 724)
                .background(.black)
        }
    }
}

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 ScreenCaptureKit.

Ownership and state

classDiagram
    ScreenRecorder *-- Logger : logger
    ScreenRecorder o-- CaptureType : captureType
    ScreenRecorder *-- Int : maximumStreamCount
    ScreenRecorder o-- Excludedwindowidsselection : excludedWindowIDsSelection

Ownership evidence

CaptureSample/ScreenRecorder.swift:43 — stored dependency or nearest verified ownership anchor

@MainActor
class ScreenRecorder: NSObject,
                      ObservableObject,
                      SCContentSharingPickerObserver {
    // ...
}

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

CaptureSample/CaptureEngine.swift:14 — representative execution boundary

struct CapturedFrame: @unchecked Sendable {
    static var invalid: CapturedFrame {
        CapturedFrame(surface: nil, contentRect: .zero, contentScale: 0, scaleFactor: 0)
    }
    // ...
}

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

CaptureSample/PowerMeter.swift:19 — representative type boundary

protocol AudioLevelProvider {
    var levels: AudioLevels { get }
}

The source explicitly defines local protocol relationships: PowerMeter → AudioLevelProvider.

Access control

Reference code

CaptureSample/CaptureEngine.swift:29 — representative boundary

class CaptureEngine: NSObject, @unchecked Sendable {
    // ...
    private let logger = Logger()
    // ...
}

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

Main application flow

Starting a capture is an asynchronous pipeline: the UI starts the recorder, the engine adapts ScreenCaptureKit callbacks into an async stream, and the recorder updates the preview for every yielded frame.

sequenceDiagram
    actor User
    participant View as ContentView
    participant Recorder as ScreenRecorder
    participant Engine as CaptureEngine
    participant Stream as SCStream
    participant Output as CaptureEngineStreamOutput
    participant Preview as CapturePreview
    User->>View: Start capture
    View->>Recorder: start()
    Recorder->>Engine: startCapture(configuration, filter)
    Engine->>Stream: addStreamOutput(...) and startCapture()
    loop each screen sample
        Stream-->>Output: didOutputSampleBuffer
        Output-->>Engine: continuation.yield(frame)
        Engine-->>Recorder: AsyncThrowingStream frame
        Recorder->>Preview: updateFrame(frame)
    end

Reference code

CaptureSample/CaptureEngine.swift:44 — startCapture

    func startCapture(configuration: SCStreamConfiguration, filter: SCContentFilter) -> AsyncThrowingStream<CapturedFrame, Error> {
        AsyncThrowingStream<CapturedFrame, Error> { continuation in
            // The stream output object. Avoid reassigning it to a new object every time startCapture is called.
            let streamOutput = CaptureEngineStreamOutput(continuation: continuation)
            self.streamOutput = streamOutput
            streamOutput.capturedFrameHandler = { continuation.yield($0) }
            streamOutput.pcmBufferHandler = { self.powerMeter.process(buffer: $0) }

            do {
                stream = SCStream(filter: filter, configuration: configuration, delegate: streamOutput)

                // Add a stream output to capture screen content.
                try stream?.addStreamOutput(streamOutput, type: .screen, sampleHandlerQueue: videoSampleBufferQueue)
                try stream?.addStreamOutput(streamOutput, type: .audio, sampleHandlerQueue: audioSampleBufferQueue)
                try stream?.addStreamOutput(streamOutput, type: .microphone, sampleHandlerQueue: micSampleBufferQueue)
                stream?.startCapture()
            } catch {
                continuation.finish(throwing: error)
            }
        }
    }

CaptureSample/ScreenRecorder.swift:195 — start

    func start() async {
        // Exit early if already running.
        guard !isRunning else { return }

        if !isSetup {
            // Starting polling for available screen content.
            await monitorAvailableContent()
            isSetup = true
        }

        // If the user enables audio capture, start monitoring the audio stream.
        if isAudioCaptureEnabled {
            startAudioMetering()
        }

        do {
            let config = streamConfiguration
            let filter = contentFilter
            // Update the running state.
            isRunning = true
            setPickerUpdate(false)
            // Start the stream and await new video frames.
            for try await frame in captureEngine.startCapture(configuration: config, filter: filter) {
                capturePreview.updateFrame(frame)
                if contentSize != frame.size {
                    // Update the content size if it changed.
                    contentSize = frame.size
                }
            }
        } catch {
            logger.error("\(error.localizedDescription)")
            // Unable to start the stream. Set the running state to false.
            isRunning = false
        }
    }

Naming conventions

• Types: App: CaptureSampleApp; Engine: CaptureEngine; Player: AudioPlayer; Provider: AudioLevelProvider, AudioLevelsProvider; Recorder: ScreenRecorder; View: AudioLevelsView, BundleIDsListView, ConfigurationView, ContentView, HeaderView.
• Protocols: AudioLevelProvider.
• Methods: monitorAvailableContent, start, stop, openRecordingFolder, startAudioMetering, stopAudioMetering, addMicrophoneOutput, removeMicrophoneOutput.
• Files: CaptureSample/CaptureSampleApp.swift, CaptureSample/ScreenRecorder.swift, CaptureSample/Views/ConfigurationView.swift, CaptureSample/CaptureEngine.swift, CaptureSample/ContentView.swift, CaptureSample/PowerMeter.swift.

Architecture takeaways

• CaptureSampleApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, ScreenCaptureKit, AVFoundation, AVFAudio 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