Processing spatial video with a custom video compositor

At a glance

Project structure

Source bundle/
└── AVFSpatialCustomVideoCompositorSample/
    ├── AVFSpatialCustomVideoCompositorSample.swift
    ├── Compositing/
    │   ├── VideoCompositionBuilder.swift
    │   ├── PixelBufferHelper.swift
    │   ├── MonoOutputCompositor.swift
    │   └── StereoOutputCompositor.swift
    ├── ContentView.swift
    ├── Views/
    │   ├── PlayerView.swift
    │   └── SettingsView.swift
    ├── Export/
    │   ├── Exporter.swift
    │   ├── ExportSessionExporter.swift
    │   └── ReaderWriterExporter.swift
    └── SampleModel.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 21 source declaration(s).

Overall architecture

flowchart LR
    N1["AVFSpatialCustomVideoCompositorSample"]
    N2["ContentView"]
    N3["SampleModel"]
    N4["AVFoundation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

AVFSpatialCustomVideoCompositorSample/AVFSpatialCustomVideoCompositorSample.swift:11 — architecture anchor

@main
struct AVFSpatialCustomVideoCompositorSample: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
                .task {
                    UserSettings.shared.registerDefaults()
                }
        }
    }
}

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
    AVFSpatialCustomVideoCompositorSample *-- Logger : logger
    VideoCompositionBuilder o-- AVAsset : asset
    VideoCompositionBuilder o-- CompositorType : compositorType
    SpatialVideoCompositionInstruction o-- AVVideoCompositionInstructionProtocol : wrappedInstruction

Ownership evidence

AVFSpatialCustomVideoCompositorSample/AVFSpatialCustomVideoCompositorSample.swift:24 — stored dependency or nearest verified ownership anchor

let logger = Logger(subsystem: "AVF-SpatialCustomVideoCompositorSample", category: "app")

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

AVFSpatialCustomVideoCompositorSample/Compositing/MonoOutputCompositor.swift:71 — representative execution boundary

class MonoOutputCompositor: NSObject, AVVideoCompositing {
    // ...
    var sourcePixelBufferAttributes: [String: any Sendable]? = [
        kCVPixelBufferPixelFormatTypeKey as String: [
            kCVPixelFormatType_420YpCbCr8BiPlanarVideoRange,
            kCVPixelFormatType_420YpCbCr10BiPlanarVideoRange
        ]
    ]
    // ...
}

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

AVFSpatialCustomVideoCompositorSample/Export/Exporter.swift:39 — representative type boundary

protocol Exporter {
    // ...
    var status: ExporterStatus { get }
    // ...
}

The source explicitly defines local protocol relationships: ExportSessionExporter → Exporter, ReaderWriterExporter → Exporter.

Access control

Reference code

AVFSpatialCustomVideoCompositorSample/Compositing/VideoCompositionBuilder.swift:12 — representative boundary

struct VideoCompositionBuilder {
    // ...
    private let asset: AVAsset
    // ...
}

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: Builder: VideoCompositionBuilder; Model: SampleModel; View: ContentView, PlayerView, SettingsView.
• Protocols: Exporter.
• Methods: build, didDismissSettings, makeUIViewController, updateUIViewController, makeNSView, updateNSView, createExporter, export.
• Files: AVFSpatialCustomVideoCompositorSample/AVFSpatialCustomVideoCompositorSample.swift, AVFSpatialCustomVideoCompositorSample/Compositing/VideoCompositionBuilder.swift, AVFSpatialCustomVideoCompositorSample/ContentView.swift, AVFSpatialCustomVideoCompositorSample/Views/PlayerView.swift, AVFSpatialCustomVideoCompositorSample/Export/Exporter.swift, AVFSpatialCustomVideoCompositorSample/SampleModel.swift.

Architecture takeaways

• AVFSpatialCustomVideoCompositorSample is the main source-visible entry or composition anchor for this sample.
• Framework work reaches AVFoundation, SwiftUI, AVKit, CoreImage 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