Capturing system audio with Core Audio taps

At a glance

Project structure

Source bundle/
└── AudioTapSample/
    ├── AudioTapSampleApp.swift
    ├── Model.swift
    ├── AudioRecorder.mm
    ├── Views/
    │   ├── ContentView.swift
    │   ├── AggregateDeviceView.swift
    │   ├── AudioIOView.swift
    │   ├── AudioProcessView.swift
    │   ├── AudioTapView.swift
    │   └── TapConfigView.swift
    ├── AudioRecorder.h
    ├── AggregateDevice.swift
    └── AudioTap.swift

Structure observations

• Architecturally prominent files are ranked from entry points and role-named declarations; resource-only paths are omitted.
• Primary languages: C/Objective-C header, Objective-C++, Swift.
• The verified tree contains 5 project/configuration file(s) and 19 source declaration(s).

Overall architecture

flowchart LR
    N1["AudioTapSampleApp"]
    N2["ContentView"]
    N3["Model"]
    N4["AudioRecorder"]
    N5["CoreAudio APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

AudioTapSample/AudioTapSampleApp.swift:10 — architecture anchor

@main
struct AudioTapSampleApp: App {
    @StateObject private var model = Model()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environmentObject(model)
        }
    }
}

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 Core Audio.

Ownership and state

classDiagram
    AudioTapSampleApp *-- Model : model
    Model o-- AudioObjectID : processSelection
    Model o-- AudioObjectID : tapSelection
    Model *-- TapConfig : tapConfiguration

Ownership evidence

AudioTapSample/AudioTapSampleApp.swift:12 — stored dependency or nearest verified ownership anchor

@main
struct AudioTapSampleApp: App {
    @StateObject private var model = Model()
    // ...
}

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

AudioTapSample/AggregateDevice.swift:63 — representative execution boundary

class AggregateDevice: AudioDevice {
    // ...
        AudioObjectAddPropertyListenerBlock(id, &deviceListAddress, DispatchQueue.main, propertiesChanged)
    // ...
}

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

AudioTapSample/AudioTapSampleApp.swift:11 — representative type boundary

@main
struct AudioTapSampleApp: App {
    @StateObject private var model = Model()
    // ...
}

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

Access control

Reference code

AudioTapSample/AggregateDevice.swift:190 — representative boundary

    private func addRemove(uid: String, action: ModifyAction, type: ListType) {
        var propertyAddress: AudioObjectPropertyAddress
        // ...
    }

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: App: AudioTapSampleApp; Model: Model; Recorder: AudioRecorder; View: AggregateDeviceView, AudioIOView, AudioProcessView, AudioTapView, ContentView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: registerListeners, unregisterListeners, loadProcessList, processStopped, loadTapList, createTap, destroyTap, loadDeviceList.
• Files: AudioTapSample/AudioTapSampleApp.swift, AudioTapSample/Model.swift, AudioTapSample/AudioRecorder.mm, AudioTapSample/Views/ContentView.swift, AudioTapSample/AudioRecorder.h, AudioTapSample/Views/AggregateDeviceView.swift.

Architecture takeaways

• AudioTapSampleApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, CoreAudio, AppKit, AudioToolbox 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