Capturing stereo audio from built-In microphones

At a glance

Project structure

Source bundle/
├── StereoAudioCapture/
│   ├── Audio/
│   │   ├── AudioController.swift
│   │   └── MeterTable.swift
│   ├── StereoLevelMeterView.swift
│   ├── AppDelegate.swift
│   ├── MainViewController.swift
│   ├── SceneDelegate.swift
│   ├── StereoLayoutView.swift
│   ├── Model/
│   │   └── StereoLayout.swift
│   └── Extensions/
│       ├── FileManagerExtensions.swift
│       └── UIViewExtensions.swift
├── Configuration/
│   └── SampleCode.xcconfig
└── StereoAudioCapture.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 6 project/configuration file(s) and 18 source declaration(s).

Overall architecture

flowchart LR
    N1["AppDelegate"]
    N2["AudioController"]
    N3["StereoLevelsProvider"]
    N4["UIKit / AVFoundation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

StereoAudioCapture/AppDelegate.swift:10 — architecture anchor

@UIApplicationMain
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 AVFAudio.

Ownership and state

classDiagram
    RecordingOption *-- String : name
    RecordingOption *-- String : dataSourceName
    AudioController *-- Array : recordingOptions
    AudioController o-- AudioControllerDelegate : delegate

Ownership evidence

StereoAudioCapture/Audio/AudioController.swift:39 — stored dependency or nearest verified ownership anchor

struct RecordingOption: Comparable {
    let name: String
    fileprivate let dataSourceName: String
    static func < (lhs: RecordingOption, rhs: RecordingOption) -> Bool {
        lhs.name < rhs.name
    }
}

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.

No source-visible execution, scheduling, or synchronization boundary was found in the indexed source.

@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.

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

StereoAudioCapture/Audio/AudioController.swift:12 — representative type boundary

protocol AudioControllerDelegate: AnyObject {
    func audioControllerDidStopPlaying()
}

The source explicitly defines local protocol relationships: AudioController → StereoLevelsProvider, AVAudioRecorder → Meterable, AVAudioPlayer → Meterable, MainViewController → AudioControllerDelegate.

Access control

Reference code

StereoAudioCapture/Audio/AudioController.swift:40 — representative boundary

struct RecordingOption: Comparable {
    // ...
    fileprivate let dataSourceName: String
    // ...
}

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: AudioController, MainViewController; Delegate: AppDelegate, AudioControllerDelegate, SceneDelegate; Provider: StereoLevelsProvider; View: LevelMeterView, StereoLayoutView, StereoLevelMeterView.
• Protocols: AudioControllerDelegate, StereoLevelsProvider, Meterable.
• Methods: audioControllerDidStopPlaying, setupAudioSession, enableBuiltInMic, selectRecordingOption, setupRecorder, record, stopRecording, play.
• Files: StereoAudioCapture/Audio/AudioController.swift, StereoAudioCapture/StereoLevelMeterView.swift, StereoAudioCapture/AppDelegate.swift, StereoAudioCapture/MainViewController.swift, StereoAudioCapture/SceneDelegate.swift, StereoAudioCapture/StereoLayoutView.swift.

Architecture takeaways

• AppDelegate is the main source-visible entry or composition anchor for this sample.
• Framework work reaches UIKit, AVFoundation, CoreGraphics 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