Using HEVC video with alpha

At a glance

Project structure

HEVC-Videos-With-Alpha.xcworkspace
├── HEVC-Videos-With-Alpha-Playback/
│   ├── ViewController.swift
│   └── Resources/
├── HEVC-Videos-With-Alpha-AssetWriting/
│   ├── AppDelegate.swift
│   └── Resources/
└── HEVC-Videos-With-Alpha-Exports/
    ├── main.swift
    └── Resources/

These are complementary demonstrations, not layers of a single application. Architecture and ownership therefore need to be read per target.

Overall architecture

flowchart LR
    Workspace["Sample workspace"] --> Playback["Playback target"]
    Workspace --> Writing["Asset-writing target"]
    Workspace --> Exports["CLI export target"]
    Playback --> Sprite["SKVideoNode + AVPlayer"]
    Writing --> Render["SceneKit / Metal frames"]
    Render --> Writer["AVAssetWriter HEVC alpha"]
    Exports --> Session["AVAssetExportSession"]
    Exports --> Filter["Core Image chroma key"]

Reference code

HEVC-Videos-With-Alpha-Playback/HEVC-Videos-With-Alpha-Playback/ViewController.swift:31 — the playback target is deliberately direct (abridged).

guard let alphaMovieURL = Bundle.main.url(
    forResource: "puppets_with_alpha_hevc", withExtension: "mov"
) else { return }
videoPlayer = AVPlayer(url: alphaMovieURL)
let video = SKVideoNode(avPlayer: videoPlayer)
scene.addChild(video)
videoPlayer.play()

The playback app composes the alpha video over a SpriteKit scene. It does not share services with the writing or export targets.

Ownership and state

classDiagram
    PlaybackViewController *-- AVPlayer
    PlaybackViewController *-- SKVideoNode : creates
    AssetWritingAppDelegate *-- SCNRenderer
    AssetWritingAppDelegate *-- CVMetalTextureCache
    AssetWritingAppDelegate --> AVAssetWriter : per export
    ExportMain --> AVAssetExportSession : per operation

Ownership evidence

HEVC-Videos-With-Alpha-AssetWriting/HEVC-Videos-With-Alpha-AssetWriting/AppDelegate.swift:31 — the writing app owns long-lived renderer resources and creates writer resources per export (abridged).

let renderer = SCNRenderer(device: nil, options: nil)
var lampMaterials: SCNNode!
var metalTextureCache: CVMetalTextureCache!
var frameCounter = 0

func makeAssetWriter(outputURL: URL, fileType: AVFileType) throws
    -> (assetWriter: AVAssetWriter,
        writerInput: AVAssetWriterInput,
        adaptor: AVAssetWriterInputPixelBufferAdaptor) {
    // ... creates one writer graph for an export
}

Class and protocol design

classDiagram
    class NSApplicationDelegate {
        <<protocol>>
    }
    class SCNSceneRendererDelegate {
        <<protocol>>
    }
    AssetWritingAppDelegate ..|> NSApplicationDelegate
    AssetWritingAppDelegate ..|> SCNSceneRendererDelegate
    PlaybackViewController --|> NSViewController

Reference code

HEVC-Videos-With-Alpha-AssetWriting/HEVC-Videos-With-Alpha-AssetWriting/AppDelegate.swift:21 — the writing app uses framework protocols, not an app-defined abstraction (abridged).

@NSApplicationMain
class AppDelegate: NSObject,
                   NSApplicationDelegate,
                   SCNSceneRendererDelegate {
    // ...
    func renderer(_ renderer: SCNSceneRenderer,
                  updateAtTime time: TimeInterval) {
        let angle = CGFloat(Double.pi * 2 * time / ExportSettings.duration.seconds)
        lampMaterials.eulerAngles = SCNVector3(x: 0, y: angle, z: 0)
    }
}

No custom protocol-oriented layer exists. The sample relies on AVFoundation, SceneKit, SpriteKit, and AppKit protocol/class contracts directly.

Access control

HEVC-Videos-With-Alpha-Exports/HEVC-Videos-With-Alpha-Exports/main.swift:14 (abridged):

extension AVAssetExportSession.Status: CustomStringConvertible {
    public var description: String {
        switch self {
        case .completed: return "completed"
        case .failed: return "failed"
        // ...
        }
    }
}

Logic ownership and placement

Design patterns

Naming conventions

• Target names describe use cases: Playback, AssetWriting, and Exports.
• Functions name source/destination transformations (exportToHEVCWithAlpha..., exportFromHEVCWithAlphaToAVC...).
• Fixed encoding dimensions/timing live under ExportSettings.
• Framework-generic names (AppDelegate, ViewController) reflect the very small target scope.

Architecture takeaways

• Read this archive as three small pipelines, not one app architecture.
• Keep writer/input/adaptor lifetime together for a single export operation.
• Local helper functions can be sufficient boundaries for a recipe-style command-line target.
• App-defined protocol abstraction is absent; framework protocols are the collaboration contracts.

Source map

Source caveat: the targets intentionally duplicate small amounts of setup and do not form a reusable HEVC-alpha library.

• Official Apple documentation