Rendering stereoscopic video with RealityKit

At a glance

Project structure

Source bundle/
├── RealityKit-Playback-AVSampleBufferVideoRenderer/
│   ├── RealityKitPlaybackApp.swift
│   ├── Models/
│   │   ├── PlayerModel.swift
│   │   ├── LoopingVideoPlayer.swift
│   │   ├── SerialProcessor.swift
│   │   └── StereoMetadata.swift
│   ├── Views/
│   │   └── ContentView.swift
│   └── Info.plist
├── Configuration/
│   └── SampleCode.xcconfig
└── RealityKit-Playback-AVSampleBufferVideoRenderer.xcodeproj/
    ├── .xcodesamplecode.plist
    └── project.pbxproj

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 8 source declaration(s).

Overall architecture

flowchart LR
    N1["RealityKitPlaybackApp"]
    N2["ContentView"]
    N3["PlayerModel"]
    N4["SerialProcessor"]
    N5["AVFoundation / SwiftUI APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4
    N4 --> N5

Reference code

RealityKit-Playback-AVSampleBufferVideoRenderer/RealityKitPlaybackApp.swift:11 — architecture anchor

@main
struct RealityKitPlaybackApp: App {
    /// An object that controls the video playback behavior.
    @State private var player = PlayerModel()

    var body: some Scene {
        WindowGroup {
            ContentView()
                .environment(player)
                .frame(width: 1600, height: 900)
        }
        // Expressly constrain window size to that of its content.
        .windowResizability(.contentSize)
        // Disable background glass.
        .windowStyle(.plain)
    }
}

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 RealityKit.

Ownership and state

classDiagram
    RealityKitPlaybackApp *-- PlayerModel : player
    PlayerModel o-- Bundle : resourceURL
    PlayerModel o-- LoopingVideoPlayer : player
    LoopingVideoPlayer *-- AVSampleBufferRenderSynchronizer : synchronizer

Ownership evidence

RealityKit-Playback-AVSampleBufferVideoRenderer/RealityKitPlaybackApp.swift:14 — stored dependency or nearest verified ownership anchor

@main
struct RealityKitPlaybackApp: App {
    // ...
    @State private var player = PlayerModel()
    // ...
}

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

RealityKit-Playback-AVSampleBufferVideoRenderer/Models/LoopingVideoPlayer.swift:46 — representative execution boundary

    func load() async throws {
        // ...
        let duration = try await asset.load(.duration)
        // ...
    }

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

RealityKit-Playback-AVSampleBufferVideoRenderer/RealityKitPlaybackApp.swift:12 — representative type boundary

@main
struct RealityKitPlaybackApp: App {
    // ...
    @State private var player = PlayerModel()
    // ...
}

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

Access control

Reference code

RealityKit-Playback-AVSampleBufferVideoRenderer/Models/LoopingVideoPlayer.swift:13 — representative boundary

final class LoopingVideoPlayer {
    // ...
    private let synchronizer = AVSampleBufferRenderSynchronizer()
    // ...
}

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
    participant SerialProcessor
    participant asset
    participant videoTrack
    participant videoTrackOutputProvider
    SerialProcessor->>asset: loadTracks()
    SerialProcessor->>videoTrack: load()
    SerialProcessor-->>SerialProcessor: _() stream
    SerialProcessor->>videoTrackOutputProvider: next()

Reference code

RealityKit-Playback-AVSampleBufferVideoRenderer/Models/SerialProcessor.swift:96 — process()

        for await _ in mediaDataReadyStream() {
            try Task.checkCancellation()

            while videoRenderer.isReadyForMoreMediaData {
                guard let sampleBuffer = try await videoTrackOutputProvider.next() else {
                    return
                }

                if let transformedBuffer = try transform(from: sampleBuffer, with: pixelBufferPool, in: transferSession) {
                    videoRenderer.enqueue(transformedBuffer)
                }
            }
        }

Naming conventions

• Types: App: RealityKitPlaybackApp; Model: PlayerModel; Player: LoopingVideoPlayer; Processor: SerialProcessor; View: ContentView.
• Protocols: no local protocol declaration in the scanned source.
• Methods: load, play, stop, enqueueProcessor, loop, process, mediaDataReadyStream, transform.
• Files: RealityKit-Playback-AVSampleBufferVideoRenderer/RealityKitPlaybackApp.swift, RealityKit-Playback-AVSampleBufferVideoRenderer/Models/PlayerModel.swift, RealityKit-Playback-AVSampleBufferVideoRenderer/Models/LoopingVideoPlayer.swift, RealityKit-Playback-AVSampleBufferVideoRenderer/Models/SerialProcessor.swift, RealityKit-Playback-AVSampleBufferVideoRenderer/Views/ContentView.swift, RealityKit-Playback-AVSampleBufferVideoRenderer/Models/StereoMetadata.swift.

Architecture takeaways

• RealityKitPlaybackApp is the main source-visible entry or composition anchor for this sample.
• Framework work reaches AVFoundation, SwiftUI, CoreVideo, CoreMedia 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