Building an audio sequencer to arrange and play clips

At a glance

Project structure

Source bundle/
└── ClipLauncher/
    └── ClipLauncher/
        ├── ClipLauncherApp.swift
        ├── Models/
        │   ├── Constants.swift
        │   ├── ClipScene.swift
        │   └── AudioClip.swift
        ├── Audio/
        │   ├── ClipLoader.swift
        │   └── ClipEngine.swift
        ├── ViewModel/
        │   └── ClipLauncherViewModel.swift
        ├── Controller/
        │   └── ClipLauncherController.swift
        └── Views/
            ├── ContentView.swift
            ├── Controls/
            │   └── FaderView.swift
            ├── Grid/
            │   └── ClipSlotView.swift
            └── WaveformView.swift

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 3 project/configuration file(s) and 37 source declaration(s).

Overall architecture

flowchart LR
    N1["ClipLauncherApp"]
    N2["ContentView"]
    N3["ClipLauncherViewModel"]
    N4["ClipEngine"]
    N5["SwiftUI / AVFoundation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

ClipLauncher/ClipLauncher/ClipLauncherApp.swift:9 — architecture anchor

@main
struct ClipLauncherApp: App {
    // ...
        WindowGroup {
            ContentView()
        }
    // ...
}

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
    Constants *-- Double : defaultTempo
    Constants *-- Double : minTempo
    Constants *-- Double : maxTempo
    Constants *-- Double : minimumAnalysisDuration

Ownership evidence

ClipLauncher/ClipLauncher/Models/Constants.swift:28 — stored dependency or nearest verified ownership anchor

    enum BPM {
        // ...
        static let defaultTempo: Double = 120
        // ...
    }

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

ClipLauncher/ClipLauncher/Audio/AudioLevelTap.swift:21 — representative execution boundary

@Observable
@MainActor
public final class AudioLevelTap {
    // ...
    public private(set) var level: Float = 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

ClipLauncher/ClipLauncher/ClipLauncherApp.swift:10 — representative type boundary

@main
struct ClipLauncherApp: App {
    // ...
            ContentView()
    // ...
}

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

Access control

Reference code

ClipLauncher/ClipLauncher/Audio/AudioLevelTap.swift:24 — representative boundary

@Observable
@MainActor
public final class AudioLevelTap {
    // ...
    public private(set) var level: Float = 0
    // ...
}

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

sequenceDiagram
    actor User
    participant VM as ViewModel
    participant C as Controller
    participant E as ClipEngine
    User->>VM: Launch scene
    loop each populated track
        VM->>C: queueClip(track, clipID)
        C->>E: queue clip
    end
    VM->>C: flushLaunchQueue()
    C->>E: schedule common quantized start
    E-->>C: launch callbacks
    C-->>VM: AsyncStream clipStarted events

Reference code

ClipLauncher/ClipLauncher/ViewModel/ClipLauncherViewModel.swift:215 — launchScene

    func launchScene(sceneIndex: Int) {
        guard sceneIndex >= 0 else { return }

        // Stop any clips that are in other scenes.
        for tIndex in tracks.indices {
            for idx in tracks[tIndex].scenes.indices where idx != sceneIndex {
                if tracks[tIndex].scenes[idx].isPlaying || tracks[tIndex].scenes[idx].isLaunching {
                    controller.stop(track: tracks[tIndex].id)
                }
                clearSceneState(trackIndex: tIndex, sceneIndex: idx)
            }
        }

        // Queue all unscheduled clips in the target scene.
        for tIndex in tracks.indices {
            guard sceneIndex < tracks[tIndex].scenes.count,
                  let clip = tracks[tIndex].scenes[sceneIndex].clip,
                  !tracks[tIndex].scenes[sceneIndex].isPlaying else { continue }

            try? controller.queueClip(track: tracks[tIndex].id, clipID: clip.id)
            tracks[tIndex].scenes[sceneIndex].isLaunching = true
        }

        // Flush all queued clips with the same start time for sync.
        controller.flushLaunchQueue()
        updateBeatTimerState()
    }

Naming conventions

• Types: App: ClipLauncherApp; Controller: ClipLauncherController; Engine: ClipEngine; Loader: ClipLoader; Scene: ClipScene; View: ClipSlotView, ContentView, FaderView, WaveformView; ViewModel: ClipLauncherViewModel.
• Protocols: no local protocol declaration in the scanned source.
• Methods: load, analyzeRhythm, makeAsyncIterator, next, startEventConsumption, handleEvent, handleClipLoaded, handleClipStarted.
• Files: ClipLauncher/ClipLauncher/ClipLauncherApp.swift, ClipLauncher/ClipLauncher/Models/Constants.swift, ClipLauncher/ClipLauncher/Audio/ClipLoader.swift, ClipLauncher/ClipLauncher/ViewModel/ClipLauncherViewModel.swift, ClipLauncher/ClipLauncher/Audio/ClipEngine.swift, ClipLauncher/ClipLauncher/Controller/ClipLauncherController.swift.

Architecture takeaways

• ClipLauncherApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches SwiftUI, AVFoundation, Accelerate, UniformTypeIdentifiers 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