Editor
EditorProvider, Preview, AssetPanel, transform overlays, text editing, and the transition system.
EditorProvider
EditorProvider creates and wires the TimelineEngine, PlaybackEngine, and all Zustand stores. It must wrap all components that use engine hooks.
import { EditorProvider, type InitialTrackConfig } from '@elah/editor'
const tracks: InitialTrackConfig[] = [
{ kind: 'video', name: 'Video / Image' },
{ kind: 'audio', name: 'Audio' },
{ kind: 'elements', name: 'Elements' },
]
function App() {
return (
<EditorProvider
fps={30} // frames per second (required)
initialTracks={tracks}
>
{/* All children can access engine + stores */}
</EditorProvider>
)
}| Prop | Type | Description |
|---|---|---|
| fps | number | Frames per second (e.g. 30, 60, 24) |
| initialTracks | InitialTrackConfig[] | Track layout to initialize the engine with |
| children | ReactNode | All components that need engine access |
Preview
<Preview> mounts the WebGL2 renderer and drives the RAF playback loop. It reads resolved scenes from resolveTimeline and composites video, image, and text layers. Transform overlays are painted on top automatically.
import {
Preview,
createDefaultDemuxerFactory,
type PreviewHandle,
} from '@elah/editor'
import { useRef } from 'react'
// Build the factory once outside the component
const demuxerFactory = createDefaultDemuxerFactory()
function MyPreview() {
const ref = useRef<PreviewHandle>(null)
// PreviewHandle exposes:
// ref.current.getCanvas() → HTMLCanvasElement | null
// ref.current.getRenderer() → GpuRenderer | null
return (
<Preview
ref={ref}
demuxerFactory={demuxerFactory}
enableAudio={true} // default: true
style={{ flex: 1 }}
/>
)
}The canvas is letterboxed to the project stage aspect ratio. Off-aspect clips are contained (never stretched) within the frame using object-fit: contain semantics.
AssetPanel
The AssetPanel provides the media library UI. Features: file import via button or drag-drop, filmstrip thumbnail generation, audio waveform visualization, and drag-to-timeline for clip creation.
import { AssetPanel } from '@elah/editor'
// Minimal usage
<AssetPanel style={{ width: 240, minHeight: 0, overflowY: 'auto' }} />
// The panel uses useMediaLibrary() internally. The hook returns the assets
// plus import/remove helpers — importFiles takes an Iterable<File>:
import { useMediaLibrary } from '@elah/editor'
function CustomLibrary() {
const { assets, importFiles, removeAsset } = useMediaLibrary()
const handleFileDrop = async (files: FileList) => {
const result = await importFiles(files)
console.log('imported:', result.imported)
console.log('skipped:', result.skipped)
}
return (
<div onDrop={(e) => handleFileDrop(e.dataTransfer.files)}>
{assets.map((asset) => (
<div key={asset.id}>{asset.name}</div>
))}
</div>
)
}Transforms
Every clip has an optional transform property. The MediaTransformOverlay provides interactive drag-move and corner-drag uniform scale for video and image clips:
interface Transform {
x: number // position, normalized 0..1 of stage width
y: number // position, normalized 0..1 of stage height
scale: number // uniform scale factor (1 = native size)
rotation: number // radians, positive = clockwise
anchor: { x: number; y: number } // 0..1 within the clip's own box
}
// Set transform programmatically (updateClip needs the clip's trackId)
engine.updateClip(clipId, trackId, {
transform: { x: 0.5, y: 0.4, scale: 1.2, rotation: 0, anchor: { x: 0.5, y: 0.5 } },
})
// The transform flows to both renderers:
// GpuRenderer: applies to WebGL2 textured quad
// ExportWorker: applies via resolveDrawRect() placement mathMove and uniform scale are fully interactive. Rotation handle is partial — transform.rotation flows through both renderers but the interactive drag handle is not yet built.
Text Overlays
Text clips are rendered via a 2D-canvas-to-texture pipeline (GPU TextLayer). An interactive overlay (TextOverlay) handles drag, resize (re-rasterized to stay crisp), and inline-edit.
// Add a text clip. The 'text' option carries content + style
// (TextClipMetadata); it is required when type is 'text'.
engine.addClip({
trackId: textTrack.id,
type: 'text',
startFrame: 0,
durationFrames: 90,
name: 'Title',
text: {
content: 'Hello World',
fontSize: 48,
color: '#ffffff',
fontWeight: 'bold', // 'normal' | 'bold'
textAlign: 'center', // 'left' | 'center' | 'right'
fontFamily: 'Inter',
},
transform: {
x: 0.5,
y: 0.8, // lower third
scale: 1,
rotation: 0, // radians
anchor: { x: 0.5, y: 0.5 },
},
})
// Entry/exit animation lives on the clip as 'textAnimation', not on 'text'.
// Set it after creation via updateClip (in/out ramp, kind is 'fade'):
engine.updateClip(clipId, textTrack.id, {
textAnimation: { in: 'fade', out: 'fade', durationFrames: 10 },
})Transitions
Transitions use a snapshot-overlay architecture. The resolver sets fromClip.opacity and toClip.opacity; TransitionOverlay fades a frozen canvas snapshot via CSS; export mirrors with globalAlpha.
// Add a fade transition between two adjacent clips on the same track.
// trackId is required; returns the created Transition (or null if the
// clips aren't found on that track).
engine.addTransition({
fromClipId: clip1.id,
toClipId: clip2.id,
trackId: track.id,
kind: 'fade', // 'fade' | 'slide' (partial) | 'wipe' (partial)
durationFrames: 15,
easing: 'ease-out', // 'linear' | 'ease-in' | 'ease-out'
})
// Read transitions
const transitions = useTransitionsStore((s) => s.transitions)
// Remove a transition
engine.removeTransition(transitionId)Stage / Aspect Ratio
The stage aspect ratio is set on the engine and changes the canvas viewport. All clips are letterboxed to the stage. The StageBorder component shows a frame outline:
const engine = useTimelineEngine()
// setStage takes (width, height) as positional args.
// Portrait (9:16 — Reels/Shorts/TikTok)
engine.setStage(1080, 1920)
// Landscape (16:9 — YouTube)
engine.setStage(1920, 1080)
// Square (1:1)
engine.setStage(1080, 1080)
// Custom
engine.setStage(2560, 1440)