Swift Render

A code-first video engine for Swift developers.

Build motion graphics, data-driven films, and video tools with SwiftUI, Metal, and native Apple frameworks. Write scenes as functions of time, score them in Swift, and render them to MP4 on your Mac.

Swift Render is an engine and CLI. Use it directly to author films, or embed the library in your own app or workflow.

What you can build

• App launch and product videos, rendered straight from your Swift code.
• Motion graphics with native typography, analytic springs, timelines, and Metal shaders.
• Films driven by JSON props, video clips, images, voiceover, and captions.
• Audio-reactive scenes with a native Swift score, synthesis, samples, and cached local speech.
• Live-action effects using Apple Vision pose, hand tracking, and person masks. The Rotoscope demo combines these with stylized cut-outs.
• Local render workflows with parallel jobs, frame/range exports, contact sheets, and audio reports.

Feature guide · CLI reference · AI quickstart · Contributing

Quick start

Requires macOS 14+ and the Xcode 15+ toolchain. Apple silicon is recommended. The bundled prebuilt Metal library lets you use existing shaders without installing the separate Metal compiler; editing shaders needs that compiler.

git clone https://github.com/skyblanket/swift-render.git
cd swift-render
swift run swift-render list
swift run swift-render render KineticType --out out/kinetic-type.mp4

KineticType declares its own Swift soundtrack, which is synthesized and muxed automatically. An explicit --audio file overrides a scene's score.

For a short review render:

swift run swift-render check KineticType
swift run swift-render render KineticType --preview --open

check produces a contact sheet and frame/audio report. Inspect the pictures and listen to the actual export: automated checks do not establish visual or musical quality.

A scene is a function of time

import SwiftUI
import SwiftRender

public struct Hello: RenderScene {
    public static let defaultDuration: Double = 3.0

    @MainActor
    public static func body(at t: Double, duration: Double) -> some View {
        let p = Ease.spring(t, from: 0, to: 1,
                            response: 0.5, dampingFraction: 0.6)
        Text("hello.")
            .font(.system(size: 120, weight: .black))
            .foregroundStyle(.white)
            .scaleEffect(0.8 + 0.2 * p)
            .opacity(Ease.clip(t, 0, 0.4))
            .frame(maxWidth: .infinity, maxHeight: .infinity)
            .background(.black)
    }
}

Save it in Sources/SwiftRenderScenes/Hello.swift. The build plugin discovers scenes automatically. Or scaffold a scene with timeline and score hooks:

swift run swift-render new Hello
swift run swift-render check Hello
swift run swift-render render Hello --out out/hello.mp4

Keep scenes free of timers and mutable animation state. Frame time drives the output, so preview, frame export, and full render use the same scene logic.

Sound belongs in the scene

The native Score DSL places drums, melodic voices, samples, and speech on the same timeline as the visuals. Export a scene's track on its own:

swift run swift-render audio KineticType --out out/score.wav

Audio-reactive scenes read cached bass, mid, high, and RMS envelopes. Local voiceover can use macOS say or an optional Kokoro setup. The check command reports clipping, silence, and voice/music balance. See sound and media.

Vision and parallel rendering

printf '%s\n' '{"clip":"me.mov","style":"ascii"}' > roto.json
swift run swift-render render Rotoscope --props roto.json --jobs auto --out out/roto.mp4

VisionTrack analyzes body pose, hands, and person segmentation once and caches the result. --jobs splits rendering across processes and stitches chunks without re-encoding. --range a:b exports a picture-only section on the same frame grid as a full render.

These features are part of the engine, independent of any editor built on top of it. See Vision examples and render options.

Use the library in your app

Add the package and depend on its SwiftRender product:

.package(url: "https://github.com/skyblanket/swift-render", from: "0.9.0")

import SwiftRender

let recorder = Recorder(config: .init(
    fps: 60, size: .init(width: 1920, height: 1080)
))
try await recorder.render(to: outputURL, duration: 5) { t in
    MyView(t: t)
}

Call the recorder from a main-actor context. The SwiftRenderScenes product contains the demo collection and is optional for library users. Access bundled shaders through ShaderLibrary.swiftRender and resources through Bundle.swiftRender.

Repository map

Path	Purpose
Sources/SwiftRender/	Engine: rendering, timelines, audio, media, Vision, components, shaders
Sources/SwiftRenderScenes/	Demo scenes, separate from the reusable engine
Sources/SwiftRenderCLI/	Authoring, preview, checks, and export commands
Plugins/	Metal compilation and scene registration
Tests/SwiftRenderTests/	Engine tests, including determinism and audio/media tests
docs/	Guides, examples, and checked-in demo assets
tools/, scripts/	Supporting authoring and development tools
out/	Generated renders and review files; ignored by Git

Documentation index explains where to start. This layout keeps engine code, examples, and tooling separate.

Examples and community

Start with KineticType for motion and scoring, AudioBars for audio-reactive props, StyleLab for whole-frame looks, Rotoscope for Vision, and Release090 for a narrated feature reel. Use swift run swift-render list for the full scene list.

Launch film · Shader gallery · Style reel

Scope and requirements

• macOS 14+; this is a native Apple rendering stack, not a cross-platform browser renderer.
• Xcode 15+; install the separate Metal toolchain when editing shaders.
• Local rendering and preview. No hosted render farm or embeddable web player is included.
• Optional Kokoro dependencies are separate from the Swift package. macOS say works without that setup.
• Timing is designed to be deterministic and has regression tests. Do not assume byte-identical results across every OS, toolchain, font, or external media change.

For development, run swift build, swift test, and swift run swift-render smoke. See Contributing.

License

MIT. Keep the copyright and license notice with copies or substantial portions of the software. Your own app code, assets, and rendered content retain their own licenses.