Reading multiview 3D video files

At a glance

Project structure

Source bundle/
├── StereoViewer/
│   ├── StereoViewerApp.swift
│   ├── StereoViewModel.swift
│   ├── MediaDetailViewModel.swift
│   ├── LaunchView.swift
│   ├── MediaDetailView.swift
│   ├── StereoView.swift
│   └── StereoViewer.entitlements
├── Configuration/
│   └── SampleCode.xcconfig
└── StereoViewer.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 7 source declaration(s).

Overall architecture

flowchart LR
    N1["StereoViewerApp"]
    N2["LaunchView"]
    N3["MediaDetailViewModel"]
    N4["AVFoundation APIs"]
    N1 --> N2
    N2 --> N3
    N3 --> N4

Reference code

StereoViewer/StereoViewerApp.swift:10 — architecture anchor

@main
struct StereoViewerApp: App {
    var body: some Scene {
        WindowGroup {
            LaunchView()
        }
    }
}

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
    StereoViewModel o-- StereoViewModelState : state
    StereoViewModel *-- NSImage : leftEye
    StereoViewModel *-- NSImage : rightEye
    StereoViewModel o-- AVURLAsset : asset

Ownership evidence

StereoViewer/StereoViewModel.swift:22 — stored dependency or nearest verified ownership anchor

@Observable
class StereoViewModel: @unchecked Sendable {
    // ...
    @MainActor var state: StereoViewModelState = .loading
    // ...
}

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

StereoViewer/MediaDetailView.swift:11 — representative execution boundary

@MainActor
struct MediaDetailView: View {
    var mediaDetailViewModel: MediaDetailViewModel
    // ...
}

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

StereoViewer/StereoViewerApp.swift:11 — representative type boundary

@main
struct StereoViewerApp: App {
    // ...
            LaunchView()
    // ...
}

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

Access control

Reference code

StereoViewer/LaunchView.swift:11 — representative boundary

struct LaunchView: View {
    @State private var filename: URL?
    // ...
}

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 View as SwiftUI views
    participant Metadata as MediaDetailViewModel
    participant Decoder as StereoViewModel
    participant AVF as AVFoundation
    User->>View: Select MV-HEVC file
    View->>Metadata: Create with URL
    Metadata->>AVF: Load metadata
    User->>View: Continue / choose frame
    View->>Decoder: Create or readBuffer(at:)
    Decoder->>AVF: Discover track and read tagged buffers
    AVF-->>Decoder: Left/right pixel buffers
    Decoder-->>View: Ready state and eye images

Reference code

StereoViewer/StereoViewModel.swift:35 — init

    init(asset: AVURLAsset) {
        self.asset = asset
        Task.detached {
            do {
                if let track = try await asset.loadTracks(withMediaCharacteristic: .containsStereoMultiviewVideo).first {
                    self.track = track
                    self.framePresentationTimes = try presentationTimesFor(track: track, asset: asset)
                    self.duration = try await asset.load(.duration)
                    self.videoLayerIds = try await loadVideoLayerIdsForTrack(track)
                    if self.readBufferFromAsset(at: 0) {
                        self.publishState(.ready(times: self.framePresentationTimes))
                    }
                } else {
                    self.publishState(.error(message: "NO STEREO MULTIVIEW VIDEO TRACK IN ASSET"))
                }

            } catch {
                self.publishState(.error(message: error.localizedDescription))
            }
        }
    }

StereoViewer/StereoViewModel.swift:118 — readNextBufferFromAsset

    func readNextBufferFromAsset() {
        guard let assetReader, let trackOutput else {
            return
        }
        // ...
    }

Naming conventions

• Types: App: StereoViewerApp; View: LaunchView, MediaDetailView, StereoView; ViewModel: MediaDetailViewModel, StereoViewModel.
• Protocols: no local protocol declaration in the scanned source.
• Methods: publishState, readBufferFromAsset, readNextBufferFromAsset, presentationTimesFor, loadVideoLayerIdsForTrack, ready, error, loading.
• Files: StereoViewer/StereoViewerApp.swift, StereoViewer/StereoViewModel.swift, StereoViewer/MediaDetailViewModel.swift, StereoViewer/LaunchView.swift, StereoViewer/MediaDetailView.swift, StereoViewer/StereoView.swift.

Architecture takeaways

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