From 83a60926d87c6f2155c3a33cbf43233de9d489f2 Mon Sep 17 00:00:00 2001
From: Marcus Schiesser <mail@marcusschiesser.de>
Date: Thu, 19 Mar 2026 17:51:51 +0800
Subject: [PATCH] fix: center stacked screen and webcam layout

---
 src/components/video-editor/SettingsPanel.tsx |  66 +++--
 src/components/video-editor/VideoPlayback.tsx |  67 ++---
 src/components/video-editor/types.ts          |   2 +-
 .../video-editor/videoPlayback/layoutUtils.ts |  60 +++--
 src/lib/compositeLayout.test.ts               |  78 ++++++
 src/lib/compositeLayout.ts                    | 250 ++++++++++++++++++
 src/lib/exporter/frameRenderer.ts             | 100 +++----
 src/lib/exporter/gifExporter.ts               |   3 +-
 src/lib/exporter/videoExporter.ts             |   3 +-
 src/lib/webcamOverlay.test.ts                 |  63 -----
 src/lib/webcamOverlay.ts                      | 196 --------------
 11 files changed, 482 insertions(+), 406 deletions(-)
 create mode 100644 src/lib/compositeLayout.test.ts
 create mode 100644 src/lib/compositeLayout.ts
 delete mode 100644 src/lib/webcamOverlay.test.ts
 delete mode 100644 src/lib/webcamOverlay.ts

diff --git a/src/components/video-editor/SettingsPanel.tsx b/src/components/video-editor/SettingsPanel.tsx
index 500356b..3d546d0 100644
--- a/src/components/video-editor/SettingsPanel.tsx
+++ b/src/components/video-editor/SettingsPanel.tsx
@@ -36,10 +36,10 @@ import { Slider } from "@/components/ui/slider";
 import { Switch } from "@/components/ui/switch";
 import { Tabs, TabsContent, TabsList, TabsTrigger } from "@/components/ui/tabs";
 import { getAssetPath } from "@/lib/assetPath";
+import { WEBCAM_LAYOUT_PRESETS } from "@/lib/compositeLayout";
 import type { ExportFormat, ExportQuality, GifFrameRate, GifSizePreset } from "@/lib/exporter";
 import { GIF_FRAME_RATES, GIF_SIZE_PRESETS } from "@/lib/exporter";
 import { cn } from "@/lib/utils";
-import { WEBCAM_LAYOUT_PRESETS } from "@/lib/webcamOverlay";
 import { type AspectRatio } from "@/utils/aspectRatioUtils";
 import { getTestId } from "@/utils/getTestId";
 import { AnnotationSettingsPanel } from "./AnnotationSettingsPanel";
@@ -582,7 +582,47 @@ export function SettingsPanel({
 					)}
 				</div>
 
-				<Accordion type="multiple" defaultValue={["effects", "background"]} className="space-y-1">
+				<Accordion
+					type="multiple"
+					defaultValue={hasWebcam ? ["layout", "effects", "background"] : ["effects", "background"]}
+					className="space-y-1"
+				>
+					{hasWebcam && (
+						<AccordionItem
+							value="layout"
+							className="border-white/5 rounded-xl bg-white/[0.02] px-3"
+						>
+							<AccordionTrigger className="py-2.5 hover:no-underline">
+								<div className="flex items-center gap-2">
+									<Sparkles className="w-4 h-4 text-[#34B27B]" />
+									<span className="text-xs font-medium">Layout</span>
+								</div>
+							</AccordionTrigger>
+							<AccordionContent className="pb-3">
+								<div className="p-2 rounded-lg bg-white/5 border border-white/5">
+									<div className="text-[10px] font-medium text-slate-300 mb-1.5">Preset</div>
+									<Select
+										value={webcamLayoutPreset}
+										onValueChange={(value: WebcamLayoutPreset) =>
+											onWebcamLayoutPresetChange?.(value)
+										}
+									>
+										<SelectTrigger className="h-8 bg-black/20 border-white/10 text-xs">
+											<SelectValue placeholder="Select preset" />
+										</SelectTrigger>
+										<SelectContent>
+											{WEBCAM_LAYOUT_PRESETS.map((preset) => (
+												<SelectItem key={preset.value} value={preset.value} className="text-xs">
+													{preset.label}
+												</SelectItem>
+											))}
+										</SelectContent>
+									</Select>
+								</div>
+							</AccordionContent>
+						</AccordionItem>
+					)}
+
 					<AccordionItem value="effects" className="border-white/5 rounded-xl bg-white/[0.02] px-3">
 						<AccordionTrigger className="py-2.5 hover:no-underline">
 							<div className="flex items-center gap-2">
@@ -601,28 +641,6 @@ export function SettingsPanel({
 									/>
 								</div>
 							</div>
-							{hasWebcam && (
-								<div className="mb-3 p-2 rounded-lg bg-white/5 border border-white/5">
-									<div className="text-[10px] font-medium text-slate-300 mb-1.5">Webcam Layout</div>
-									<Select
-										value={webcamLayoutPreset}
-										onValueChange={(value: WebcamLayoutPreset) =>
-											onWebcamLayoutPresetChange?.(value)
-										}
-									>
-										<SelectTrigger className="h-8 bg-black/20 border-white/10 text-xs">
-											<SelectValue placeholder="Select layout" />
-										</SelectTrigger>
-										<SelectContent>
-											{WEBCAM_LAYOUT_PRESETS.map((preset) => (
-												<SelectItem key={preset.value} value={preset.value} className="text-xs">
-													{preset.label}
-												</SelectItem>
-											))}
-										</SelectContent>
-									</Select>
-								</div>
-							)}
 
 							<div className="grid grid-cols-2 gap-2">
 								<div className="p-2 rounded-lg bg-white/5 border border-white/5">
diff --git a/src/components/video-editor/VideoPlayback.tsx b/src/components/video-editor/VideoPlayback.tsx
index f576ae3..24cd187 100644
--- a/src/components/video-editor/VideoPlayback.tsx
+++ b/src/components/video-editor/VideoPlayback.tsx
@@ -20,11 +20,11 @@ import {
 } from "react";
 import { getAssetPath } from "@/lib/assetPath";
 import {
-	computeWebcamOverlayLayout,
 	getWebcamLayoutCssBoxShadow,
+	type Size,
+	type StyledRenderRect,
 	type WebcamLayoutPreset,
-	type WebcamOverlayLayout,
-} from "@/lib/webcamOverlay";
+} from "@/lib/compositeLayout";
 import {
 	type AspectRatio,
 	formatAspectRatioForCSS,
@@ -141,7 +141,6 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 		const videoRef = useRef<HTMLVideoElement | null>(null);
 		const webcamVideoRef = useRef<HTMLVideoElement | null>(null);
 		const containerRef = useRef<HTMLDivElement | null>(null);
-		const stageRef = useRef<HTMLDivElement | null>(null);
 		const appRef = useRef<Application | null>(null);
 		const videoSpriteRef = useRef<Sprite | null>(null);
 		const videoContainerRef = useRef<Container | null>(null);
@@ -151,15 +150,8 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 		const [videoReady, setVideoReady] = useState(false);
 		const overlayRef = useRef<HTMLDivElement | null>(null);
 		const focusIndicatorRef = useRef<HTMLDivElement | null>(null);
-		const [webcamLayout, setWebcamLayout] = useState<WebcamOverlayLayout | null>(null);
-		const [webcamDimensions, setWebcamDimensions] = useState<{
-			width: number;
-			height: number;
-		} | null>(null);
-		const [screenVideoDimensions, setScreenVideoDimensions] = useState<{
-			width: number;
-			height: number;
-		} | null>(null);
+		const [webcamLayout, setWebcamLayout] = useState<StyledRenderRect | null>(null);
+		const [webcamDimensions, setWebcamDimensions] = useState<Size | null>(null);
 		const currentTimeRef = useRef(0);
 		const zoomRegionsRef = useRef<ZoomRegion[]>([]);
 		const selectedZoomIdRef = useRef<string | null>(null);
@@ -269,6 +261,8 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 				lockedVideoDimensions: lockedVideoDimensionsRef.current,
 				borderRadius,
 				padding,
+				webcamDimensions,
+				webcamLayoutPreset,
 			});
 
 			if (result) {
@@ -278,6 +272,7 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 				baseOffsetRef.current = result.baseOffset;
 				baseMaskRef.current = result.maskRect;
 				cropBoundsRef.current = result.cropBounds;
+				setWebcamLayout(result.webcamRect);
 
 				// Reset camera container to identity
 				cameraContainer.scale.set(1);
@@ -290,7 +285,14 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 
 				updateOverlayForRegion(activeRegion);
 			}
-		}, [updateOverlayForRegion, cropRegion, borderRadius, padding]);
+		}, [
+			updateOverlayForRegion,
+			cropRegion,
+			borderRadius,
+			padding,
+			webcamDimensions,
+			webcamLayoutPreset,
+		]);
 
 		useEffect(() => {
 			layoutVideoContentRef.current = layoutVideoContent;
@@ -620,9 +622,6 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 				cancelAnimationFrame(videoReadyRafRef.current);
 				videoReadyRafRef.current = null;
 			}
-			if (video.videoWidth > 0 && video.videoHeight > 0) {
-				setScreenVideoDimensions({ width: video.videoWidth, height: video.videoHeight });
-			}
 		}, [videoPath]);
 
 		useEffect(() => {
@@ -952,37 +951,6 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 			};
 		}, [webcamVideoPath]);
 
-		useEffect(() => {
-			const stage = stageRef.current;
-			if (!stage || !webcamDimensions || !screenVideoDimensions) {
-				setWebcamLayout(null);
-				return;
-			}
-
-			const updateLayout = () => {
-				const layout = computeWebcamOverlayLayout({
-					stageWidth: stage.clientWidth,
-					stageHeight: stage.clientHeight,
-					videoWidth: webcamDimensions.width,
-					videoHeight: webcamDimensions.height,
-					layoutPreset: webcamLayoutPreset,
-					screenVideoWidth: screenVideoDimensions?.width,
-					screenVideoHeight: screenVideoDimensions?.height,
-				});
-				setWebcamLayout(layout);
-			};
-
-			updateLayout();
-
-			if (typeof ResizeObserver === "undefined") {
-				return;
-			}
-
-			const observer = new ResizeObserver(updateLayout);
-			observer.observe(stage);
-			return () => observer.disconnect();
-		}, [screenVideoDimensions, webcamDimensions, webcamLayoutPreset]);
-
 		useEffect(() => {
 			const webcamVideo = webcamVideoRef.current;
 			if (!webcamVideo || !webcamVideoPath) {
@@ -1096,7 +1064,6 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 
 		return (
 			<div
-				ref={stageRef}
 				className="relative rounded-sm overflow-hidden"
 				style={{
 					width: "100%",
@@ -1130,7 +1097,7 @@ const VideoPlayback = forwardRef<VideoPlaybackRef, VideoPlaybackProps>(
 								: "none",
 					}}
 				/>
-				{webcamVideoPath && screenVideoDimensions && (
+				{webcamVideoPath && (
 					<video
 						ref={webcamVideoRef}
 						src={webcamVideoPath}
diff --git a/src/components/video-editor/types.ts b/src/components/video-editor/types.ts
index 55a3ccb..5bd8f70 100644
--- a/src/components/video-editor/types.ts
+++ b/src/components/video-editor/types.ts
@@ -1,4 +1,4 @@
-import type { WebcamLayoutPreset } from "@/lib/webcamOverlay";
+import type { WebcamLayoutPreset } from "@/lib/compositeLayout";
 
 export type ZoomDepth = 1 | 2 | 3 | 4 | 5 | 6;
 export type { WebcamLayoutPreset };
diff --git a/src/components/video-editor/videoPlayback/layoutUtils.ts b/src/components/video-editor/videoPlayback/layoutUtils.ts
index 4daf8a5..166a0b9 100644
--- a/src/components/video-editor/videoPlayback/layoutUtils.ts
+++ b/src/components/video-editor/videoPlayback/layoutUtils.ts
@@ -1,4 +1,11 @@
 import { Application, Graphics, Sprite } from "pixi.js";
+import {
+	computeCompositeLayout,
+	type RenderRect,
+	type Size,
+	type StyledRenderRect,
+	type WebcamLayoutPreset,
+} from "@/lib/compositeLayout";
 import type { CropRegion } from "../types";
 
 interface LayoutParams {
@@ -11,6 +18,8 @@ interface LayoutParams {
 	lockedVideoDimensions?: { width: number; height: number } | null;
 	borderRadius?: number;
 	padding?: number;
+	webcamDimensions?: Size | null;
+	webcamLayoutPreset?: WebcamLayoutPreset;
 }
 
 interface LayoutResult {
@@ -18,7 +27,8 @@ interface LayoutResult {
 	videoSize: { width: number; height: number };
 	baseScale: number;
 	baseOffset: { x: number; y: number };
-	maskRect: { x: number; y: number; width: number; height: number };
+	maskRect: RenderRect;
+	webcamRect: StyledRenderRect | null;
 	cropBounds: { startX: number; endX: number; startY: number; endY: number };
 }
 
@@ -33,6 +43,8 @@ export function layoutVideoContent(params: LayoutParams): LayoutResult | null {
 		lockedVideoDimensions,
 		borderRadius = 0,
 		padding = 0,
+		webcamDimensions,
+		webcamLayoutPreset,
 	} = params;
 
 	const videoWidth = lockedVideoDimensions?.width || videoElement.videoWidth;
@@ -71,11 +83,19 @@ export function layoutVideoContent(params: LayoutParams): LayoutResult | null {
 	const maxDisplayWidth = width * paddingScale;
 	const maxDisplayHeight = height * paddingScale;
 
-	const scale = Math.min(
-		maxDisplayWidth / croppedVideoWidth,
-		maxDisplayHeight / croppedVideoHeight,
-		1,
-	);
+	const compositeLayout = computeCompositeLayout({
+		canvasSize: { width, height },
+		maxContentSize: { width: maxDisplayWidth, height: maxDisplayHeight },
+		screenSize: { width: croppedVideoWidth, height: croppedVideoHeight },
+		webcamSize: webcamDimensions,
+		layoutPreset: webcamLayoutPreset,
+	});
+
+	if (!compositeLayout) {
+		return null;
+	}
+
+	const scale = compositeLayout.screenRect.width / croppedVideoWidth;
 
 	videoSprite.scale.set(scale);
 
@@ -84,30 +104,25 @@ export function layoutVideoContent(params: LayoutParams): LayoutResult | null {
 	const fullVideoDisplayHeight = videoHeight * scale;
 
 	// Calculate display size of just the cropped region
-	const croppedDisplayWidth = croppedVideoWidth * scale;
-	const croppedDisplayHeight = croppedVideoHeight * scale;
-
-	// Center the cropped region in the container
-	const centerOffsetX = (width - croppedDisplayWidth) / 2;
-	const centerOffsetY = (height - croppedDisplayHeight) / 2;
-
 	// Position the full video sprite so that when we apply the mask,
 	// the cropped region appears centered
 	// The crop starts at (crop.x * videoWidth, crop.y * videoHeight) in video coordinates
 	// In display coordinates, that's (crop.x * fullVideoDisplayWidth, crop.y * fullVideoDisplayHeight)
-	// We want that point to be at centerOffsetX, centerOffsetY
-	const spriteX = centerOffsetX - crop.x * fullVideoDisplayWidth;
-	const spriteY = centerOffsetY - crop.y * fullVideoDisplayHeight;
+	// We want that point to be at screenRect.x, screenRect.y
+	const spriteX = compositeLayout.screenRect.x - crop.x * fullVideoDisplayWidth;
+	const spriteY = compositeLayout.screenRect.y - crop.y * fullVideoDisplayHeight;
 
 	videoSprite.position.set(spriteX, spriteY);
 
-	// Create a mask that only shows the cropped region (centered in container)
-	const maskX = centerOffsetX;
-	const maskY = centerOffsetY;
-
 	// Apply border radius
 	maskGraphics.clear();
-	maskGraphics.roundRect(maskX, maskY, croppedDisplayWidth, croppedDisplayHeight, borderRadius);
+	maskGraphics.roundRect(
+		compositeLayout.screenRect.x,
+		compositeLayout.screenRect.y,
+		compositeLayout.screenRect.width,
+		compositeLayout.screenRect.height,
+		borderRadius,
+	);
 	maskGraphics.fill({ color: 0xffffff });
 
 	return {
@@ -115,7 +130,8 @@ export function layoutVideoContent(params: LayoutParams): LayoutResult | null {
 		videoSize: { width: croppedVideoWidth, height: croppedVideoHeight },
 		baseScale: scale,
 		baseOffset: { x: spriteX, y: spriteY },
-		maskRect: { x: maskX, y: maskY, width: croppedDisplayWidth, height: croppedDisplayHeight },
+		maskRect: compositeLayout.screenRect,
+		webcamRect: compositeLayout.webcamRect,
 		cropBounds: { startX: cropStartX, endX: cropEndX, startY: cropStartY, endY: cropEndY },
 	};
 }
diff --git a/src/lib/compositeLayout.test.ts b/src/lib/compositeLayout.test.ts
new file mode 100644
index 0000000..5dc5339
--- /dev/null
+++ b/src/lib/compositeLayout.test.ts
@@ -0,0 +1,78 @@
+import { describe, expect, it } from "vitest";
+import { computeCompositeLayout } from "./compositeLayout";
+
+describe("computeCompositeLayout", () => {
+	it("anchors the overlay in the lower-right corner", () => {
+		const layout = computeCompositeLayout({
+			canvasSize: { width: 1920, height: 1080 },
+			screenSize: { width: 1920, height: 1080 },
+			webcamSize: { width: 1280, height: 720 },
+		});
+
+		expect(layout).not.toBeNull();
+		expect(layout!.webcamRect).not.toBeNull();
+		expect(layout!.webcamRect!.x + layout!.webcamRect!.width).toBeLessThanOrEqual(1920);
+		expect(layout!.webcamRect!.y + layout!.webcamRect!.height).toBeLessThanOrEqual(1080);
+		expect(layout!.webcamRect!.x).toBeGreaterThan(1920 / 2);
+		expect(layout!.webcamRect!.y).toBeGreaterThan(1080 / 2);
+	});
+
+	it("keeps the overlay within the configured stage fraction while preserving aspect ratio", () => {
+		const layout = computeCompositeLayout({
+			canvasSize: { width: 1280, height: 720 },
+			screenSize: { width: 1280, height: 720 },
+			webcamSize: { width: 1920, height: 1080 },
+		});
+
+		expect(layout).not.toBeNull();
+		expect(layout!.webcamRect).not.toBeNull();
+		expect(layout!.webcamRect!.width).toBeLessThanOrEqual(Math.round(1280 * 0.18) + 1);
+		expect(layout!.webcamRect!.height).toBeLessThanOrEqual(Math.round(720 * 0.18) + 1);
+		expect(
+			Math.abs(layout!.webcamRect!.width * 1080 - layout!.webcamRect!.height * 1920),
+		).toBeLessThanOrEqual(1920);
+	});
+
+	it("centers the combined screen and webcam stack in vertical stack mode", () => {
+		const layout = computeCompositeLayout({
+			canvasSize: { width: 1920, height: 1080 },
+			maxContentSize: { width: 1536, height: 864 },
+			screenSize: { width: 1920, height: 1080 },
+			webcamSize: { width: 1280, height: 720 },
+			layoutPreset: "vertical-stack",
+		});
+
+		expect(layout).not.toBeNull();
+		expect(layout?.screenRect).toEqual({
+			x: 576,
+			y: 108,
+			width: 768,
+			height: 432,
+		});
+		expect(layout?.webcamRect).toEqual({
+			x: 576,
+			y: 540,
+			width: 768,
+			height: 432,
+			borderRadius: 0,
+		});
+	});
+
+	it("keeps the screen centered and omits the webcam when dimensions are unavailable", () => {
+		const layout = computeCompositeLayout({
+			canvasSize: { width: 1920, height: 1080 },
+			maxContentSize: { width: 1536, height: 864 },
+			screenSize: { width: 1920, height: 1080 },
+			layoutPreset: "vertical-stack",
+		});
+
+		expect(layout).not.toBeNull();
+		expect(layout?.screenRect).toEqual({
+			x: 192,
+			y: 108,
+			width: 1536,
+			height: 864,
+		});
+		expect(layout?.webcamRect).toBeNull();
+	});
+});
diff --git a/src/lib/compositeLayout.ts b/src/lib/compositeLayout.ts
new file mode 100644
index 0000000..2b12b03
--- /dev/null
+++ b/src/lib/compositeLayout.ts
@@ -0,0 +1,250 @@
+export interface RenderRect {
+	x: number;
+	y: number;
+	width: number;
+	height: number;
+}
+
+export interface StyledRenderRect extends RenderRect {
+	borderRadius: number;
+}
+
+export interface Size {
+	width: number;
+	height: number;
+}
+
+export type WebcamLayoutPreset = "picture-in-picture" | "vertical-stack";
+
+export interface WebcamLayoutShadow {
+	color: string;
+	blur: number;
+	offsetX: number;
+	offsetY: number;
+}
+
+interface BorderRadiusRule {
+	max: number;
+	min: number;
+	fraction: number;
+}
+
+interface OverlayTransform {
+	type: "overlay";
+	maxStageFraction: number;
+	marginFraction: number;
+	minMargin: number;
+	minSize: number;
+}
+
+interface StackTransform {
+	type: "stack";
+	gap: number;
+}
+
+export interface WebcamLayoutPresetDefinition {
+	label: string;
+	transform: OverlayTransform | StackTransform;
+	borderRadius: BorderRadiusRule;
+	shadow: WebcamLayoutShadow | null;
+}
+
+export interface WebcamCompositeLayout {
+	screenRect: RenderRect;
+	webcamRect: StyledRenderRect | null;
+}
+
+const MAX_STAGE_FRACTION = 0.18;
+const MARGIN_FRACTION = 0.02;
+const MIN_SIZE = 96;
+const MAX_BORDER_RADIUS = 24;
+const WEBCAM_LAYOUT_PRESET_MAP: Record<WebcamLayoutPreset, WebcamLayoutPresetDefinition> = {
+	"picture-in-picture": {
+		label: "Picture in Picture",
+		transform: {
+			type: "overlay",
+			maxStageFraction: MAX_STAGE_FRACTION,
+			marginFraction: MARGIN_FRACTION,
+			minMargin: 12,
+			minSize: MIN_SIZE,
+		},
+		borderRadius: {
+			max: MAX_BORDER_RADIUS,
+			min: 12,
+			fraction: 0.12,
+		},
+		shadow: {
+			color: "rgba(0,0,0,0.35)",
+			blur: 24,
+			offsetX: 0,
+			offsetY: 10,
+		},
+	},
+	"vertical-stack": {
+		label: "Vertical Stack",
+		transform: {
+			type: "stack",
+			gap: 0,
+		},
+		borderRadius: {
+			max: 0,
+			min: 0,
+			fraction: 0,
+		},
+		shadow: null,
+	},
+};
+
+export const WEBCAM_LAYOUT_PRESETS = Object.entries(WEBCAM_LAYOUT_PRESET_MAP).map(
+	([value, preset]) => ({
+		value: value as WebcamLayoutPreset,
+		label: preset.label,
+	}),
+);
+
+export function getWebcamLayoutPresetDefinition(
+	preset: WebcamLayoutPreset = "picture-in-picture",
+): WebcamLayoutPresetDefinition {
+	return WEBCAM_LAYOUT_PRESET_MAP[preset];
+}
+
+export function getWebcamLayoutCssBoxShadow(
+	preset: WebcamLayoutPreset = "picture-in-picture",
+): string {
+	const shadow = getWebcamLayoutPresetDefinition(preset).shadow;
+	return shadow
+		? `${shadow.offsetX}px ${shadow.offsetY}px ${shadow.blur}px ${shadow.color}`
+		: "none";
+}
+
+export function computeCompositeLayout(params: {
+	canvasSize: Size;
+	maxContentSize?: Size;
+	screenSize: Size;
+	webcamSize?: Size | null;
+	layoutPreset?: WebcamLayoutPreset;
+}): WebcamCompositeLayout | null {
+	const {
+		canvasSize,
+		maxContentSize = canvasSize,
+		screenSize,
+		webcamSize,
+		layoutPreset = "picture-in-picture",
+	} = params;
+	const { width: canvasWidth, height: canvasHeight } = canvasSize;
+	const { width: maxContentWidth, height: maxContentHeight } = maxContentSize;
+	const { width: screenWidth, height: screenHeight } = screenSize;
+	const webcamWidth = webcamSize?.width;
+	const webcamHeight = webcamSize?.height;
+	const preset = getWebcamLayoutPresetDefinition(layoutPreset);
+
+	if (canvasWidth <= 0 || canvasHeight <= 0 || screenWidth <= 0 || screenHeight <= 0) {
+		return null;
+	}
+
+	if (preset.transform.type === "stack") {
+		if (!webcamWidth || !webcamHeight || webcamWidth <= 0 || webcamHeight <= 0) {
+			return {
+				screenRect: centerRect({
+					canvasSize,
+					size: screenSize,
+					maxSize: maxContentSize,
+				}),
+				webcamRect: null,
+			};
+		}
+
+		const gap = preset.transform.gap;
+		const normalizedWebcamHeight = webcamHeight * (screenWidth / webcamWidth);
+		const combinedHeight = screenHeight + gap + normalizedWebcamHeight;
+		const scale = Math.min(maxContentWidth / screenWidth, maxContentHeight / combinedHeight, 1);
+		const clampedScale = Number.isFinite(scale) && scale > 0 ? scale : 1;
+		const resolvedScreenHeight = Math.round(screenHeight * clampedScale);
+		const resolvedScreenWidth = Math.round(screenWidth * clampedScale);
+		const resolvedWebcamHeight = Math.round(normalizedWebcamHeight * clampedScale);
+		const resolvedGap = Math.round(gap * clampedScale);
+		const totalHeight = resolvedScreenHeight + resolvedGap + resolvedWebcamHeight;
+		const top = Math.max(0, Math.floor((canvasHeight - totalHeight) / 2));
+		const left = Math.max(0, Math.floor((canvasWidth - resolvedScreenWidth) / 2));
+		const screenRect = {
+			x: left,
+			y: top,
+			width: resolvedScreenWidth,
+			height: resolvedScreenHeight,
+		};
+
+		return {
+			screenRect,
+			webcamRect: {
+				x: left,
+				y: top + resolvedScreenHeight + resolvedGap,
+				width: resolvedScreenWidth,
+				height: resolvedWebcamHeight,
+				borderRadius: Math.min(
+					preset.borderRadius.max,
+					Math.max(
+						preset.borderRadius.min,
+						Math.round(
+							Math.min(resolvedScreenWidth, resolvedWebcamHeight) * preset.borderRadius.fraction,
+						),
+					),
+				),
+			},
+		};
+	}
+
+	const transform = preset.transform;
+	const screenRect = centerRect({
+		canvasSize,
+		size: screenSize,
+		maxSize: maxContentSize,
+	});
+
+	if (!webcamWidth || !webcamHeight || webcamWidth <= 0 || webcamHeight <= 0) {
+		return { screenRect, webcamRect: null };
+	}
+
+	const margin = Math.max(
+		transform.minMargin,
+		Math.round(Math.min(canvasWidth, canvasHeight) * transform.marginFraction),
+	);
+	const maxWidth = Math.max(transform.minSize, canvasWidth * transform.maxStageFraction);
+	const maxHeight = Math.max(transform.minSize, canvasHeight * transform.maxStageFraction);
+	const scale = Math.min(maxWidth / webcamWidth, maxHeight / webcamHeight);
+	const width = Math.round(webcamWidth * scale);
+	const height = Math.round(webcamHeight * scale);
+
+	return {
+		screenRect,
+		webcamRect: {
+			x: Math.max(0, Math.round(canvasWidth - margin - width)),
+			y: Math.max(0, Math.round(canvasHeight - margin - height)),
+			width,
+			height,
+			borderRadius: Math.min(
+				preset.borderRadius.max,
+				Math.max(
+					preset.borderRadius.min,
+					Math.round(Math.min(width, height) * preset.borderRadius.fraction),
+				),
+			),
+		},
+	};
+}
+
+function centerRect(params: { canvasSize: Size; size: Size; maxSize: Size }): RenderRect {
+	const { canvasSize, size, maxSize } = params;
+	const { width: canvasWidth, height: canvasHeight } = canvasSize;
+	const { width, height } = size;
+	const { width: maxWidth, height: maxHeight } = maxSize;
+	const scale = Math.min(maxWidth / width, maxHeight / height, 1);
+	const resolvedWidth = Math.round(width * scale);
+	const resolvedHeight = Math.round(height * scale);
+
+	return {
+		x: Math.max(0, Math.floor((canvasWidth - resolvedWidth) / 2)),
+		y: Math.max(0, Math.floor((canvasHeight - resolvedHeight) / 2)),
+		width: resolvedWidth,
+		height: resolvedHeight,
+	};
+}
diff --git a/src/lib/exporter/frameRenderer.ts b/src/lib/exporter/frameRenderer.ts
index f42edcb..5ce5bfa 100644
--- a/src/lib/exporter/frameRenderer.ts
+++ b/src/lib/exporter/frameRenderer.ts
@@ -31,7 +31,12 @@ import {
 	createMotionBlurState,
 	type MotionBlurState,
 } from "@/components/video-editor/videoPlayback/zoomTransform";
-import { computeWebcamOverlayLayout, getWebcamLayoutPresetDefinition } from "@/lib/webcamOverlay";
+import {
+	computeCompositeLayout,
+	getWebcamLayoutPresetDefinition,
+	type Size,
+	type StyledRenderRect,
+} from "@/lib/compositeLayout";
 import { renderAnnotations } from "./annotationRenderer";
 
 interface FrameRenderConfig {
@@ -48,8 +53,7 @@ interface FrameRenderConfig {
 	cropRegion: CropRegion;
 	videoWidth: number;
 	videoHeight: number;
-	webcamWidth?: number;
-	webcamHeight?: number;
+	webcamSize?: Size | null;
 	webcamLayoutPreset?: WebcamLayoutPreset;
 	annotationRegions?: AnnotationRegion[];
 	speedRegions?: SpeedRegion[];
@@ -73,6 +77,7 @@ interface LayoutCache {
 	baseScale: number;
 	baseOffset: { x: number; y: number };
 	maskRect: { x: number; y: number; width: number; height: number };
+	webcamRect: StyledRenderRect | null;
 }
 
 // Renders video frames with all effects (background, zoom, crop, blur, shadow) to an offscreen canvas for export.
@@ -417,7 +422,16 @@ export class FrameRenderer {
 		const paddingScale = 1.0 - (padding / 100) * 0.4;
 		const viewportWidth = width * paddingScale;
 		const viewportHeight = height * paddingScale;
-		const scale = Math.min(viewportWidth / croppedVideoWidth, viewportHeight / croppedVideoHeight);
+		const compositeLayout = computeCompositeLayout({
+			canvasSize: { width, height },
+			maxContentSize: { width: viewportWidth, height: viewportHeight },
+			screenSize: { width: croppedVideoWidth, height: croppedVideoHeight },
+			webcamSize: this.config.webcamSize,
+			layoutPreset: this.config.webcamLayoutPreset,
+		});
+		if (!compositeLayout) return;
+
+		const scale = compositeLayout.screenRect.width / croppedVideoWidth;
 
 		// Position video sprite
 		this.videoSprite.width = videoWidth * scale;
@@ -429,12 +443,10 @@ export class FrameRenderer {
 		this.videoSprite.y = -cropPixelY;
 
 		// Position video container
-		const croppedDisplayWidth = croppedVideoWidth * scale;
-		const croppedDisplayHeight = croppedVideoHeight * scale;
-		const centerOffsetX = (width - croppedDisplayWidth) / 2;
-		const centerOffsetY = (height - croppedDisplayHeight) / 2;
-		this.videoContainer.x = centerOffsetX;
-		this.videoContainer.y = centerOffsetY;
+		const croppedDisplayWidth = compositeLayout.screenRect.width;
+		const croppedDisplayHeight = compositeLayout.screenRect.height;
+		this.videoContainer.x = compositeLayout.screenRect.x;
+		this.videoContainer.y = compositeLayout.screenRect.y;
 
 		// scale border radius by export/preview canvas ratio
 		const previewWidth = this.config.previewWidth || 1920;
@@ -457,8 +469,9 @@ export class FrameRenderer {
 			stageSize: { width, height },
 			videoSize: { width: croppedVideoWidth, height: croppedVideoHeight },
 			baseScale: scale,
-			baseOffset: { x: centerOffsetX, y: centerOffsetY },
-			maskRect: { x: 0, y: 0, width: croppedDisplayWidth, height: croppedDisplayHeight },
+			baseOffset: { x: compositeLayout.screenRect.x, y: compositeLayout.screenRect.y },
+			maskRect: compositeLayout.screenRect,
+			webcamRect: compositeLayout.webcamRect,
 		};
 	}
 
@@ -630,41 +643,36 @@ export class FrameRenderer {
 			ctx.drawImage(videoCanvas, 0, 0, w, h);
 		}
 
-		if (webcamFrame && this.config.webcamWidth && this.config.webcamHeight) {
-			const layout = computeWebcamOverlayLayout({
-				stageWidth: w,
-				stageHeight: h,
-				videoWidth: this.config.webcamWidth,
-				videoHeight: this.config.webcamHeight,
-				layoutPreset: this.config.webcamLayoutPreset,
-				screenVideoWidth: this.config.videoWidth,
-				screenVideoHeight: this.config.videoHeight,
-			});
-
-			if (layout) {
-				const preset = getWebcamLayoutPresetDefinition(this.config.webcamLayoutPreset);
-				ctx.save();
-				ctx.beginPath();
-				ctx.roundRect(layout.x, layout.y, layout.width, layout.height, layout.borderRadius);
-				ctx.closePath();
-				if (preset.shadow) {
-					ctx.shadowColor = preset.shadow.color;
-					ctx.shadowBlur = preset.shadow.blur;
-					ctx.shadowOffsetX = preset.shadow.offsetX;
-					ctx.shadowOffsetY = preset.shadow.offsetY;
-				}
-				ctx.fillStyle = "#000000";
-				ctx.fill();
-				ctx.clip();
-				ctx.drawImage(
-					webcamFrame as unknown as CanvasImageSource,
-					layout.x,
-					layout.y,
-					layout.width,
-					layout.height,
-				);
-				ctx.restore();
+		const webcamRect = this.layoutCache?.webcamRect ?? null;
+		if (webcamFrame && webcamRect) {
+			const preset = getWebcamLayoutPresetDefinition(this.config.webcamLayoutPreset);
+			ctx.save();
+			ctx.beginPath();
+			ctx.roundRect(
+				webcamRect.x,
+				webcamRect.y,
+				webcamRect.width,
+				webcamRect.height,
+				webcamRect.borderRadius,
+			);
+			ctx.closePath();
+			if (preset.shadow) {
+				ctx.shadowColor = preset.shadow.color;
+				ctx.shadowBlur = preset.shadow.blur;
+				ctx.shadowOffsetX = preset.shadow.offsetX;
+				ctx.shadowOffsetY = preset.shadow.offsetY;
 			}
+			ctx.fillStyle = "#000000";
+			ctx.fill();
+			ctx.clip();
+			ctx.drawImage(
+				webcamFrame as unknown as CanvasImageSource,
+				webcamRect.x,
+				webcamRect.y,
+				webcamRect.width,
+				webcamRect.height,
+			);
+			ctx.restore();
 		}
 	}
 
diff --git a/src/lib/exporter/gifExporter.ts b/src/lib/exporter/gifExporter.ts
index 1d7c451..f19da5b 100644
--- a/src/lib/exporter/gifExporter.ts
+++ b/src/lib/exporter/gifExporter.ts
@@ -138,8 +138,7 @@ export class GifExporter {
 				cropRegion: this.config.cropRegion,
 				videoWidth: videoInfo.width,
 				videoHeight: videoInfo.height,
-				webcamWidth: webcamInfo?.width,
-				webcamHeight: webcamInfo?.height,
+				webcamSize: webcamInfo ? { width: webcamInfo.width, height: webcamInfo.height } : null,
 				webcamLayoutPreset: this.config.webcamLayoutPreset,
 				annotationRegions: this.config.annotationRegions,
 				speedRegions: this.config.speedRegions,
diff --git a/src/lib/exporter/videoExporter.ts b/src/lib/exporter/videoExporter.ts
index 7cb3260..aaa4d45 100644
--- a/src/lib/exporter/videoExporter.ts
+++ b/src/lib/exporter/videoExporter.ts
@@ -87,8 +87,7 @@ export class VideoExporter {
 				cropRegion: this.config.cropRegion,
 				videoWidth: videoInfo.width,
 				videoHeight: videoInfo.height,
-				webcamWidth: webcamInfo?.width,
-				webcamHeight: webcamInfo?.height,
+				webcamSize: webcamInfo ? { width: webcamInfo.width, height: webcamInfo.height } : null,
 				webcamLayoutPreset: this.config.webcamLayoutPreset,
 				annotationRegions: this.config.annotationRegions,
 				speedRegions: this.config.speedRegions,
diff --git a/src/lib/webcamOverlay.test.ts b/src/lib/webcamOverlay.test.ts
deleted file mode 100644
index 5edb9e2..0000000
--- a/src/lib/webcamOverlay.test.ts
+++ /dev/null
@@ -1,63 +0,0 @@
-import { describe, expect, it } from "vitest";
-import { computeWebcamOverlayLayout } from "./webcamOverlay";
-
-describe("computeWebcamOverlayLayout", () => {
-	it("anchors the overlay in the lower-right corner", () => {
-		const layout = computeWebcamOverlayLayout({
-			stageWidth: 1920,
-			stageHeight: 1080,
-			videoWidth: 1280,
-			videoHeight: 720,
-		});
-
-		expect(layout).not.toBeNull();
-		expect(layout!.x + layout!.width).toBeLessThanOrEqual(1920);
-		expect(layout!.y + layout!.height).toBeLessThanOrEqual(1080);
-		expect(layout!.x).toBeGreaterThan(1920 / 2);
-		expect(layout!.y).toBeGreaterThan(1080 / 2);
-	});
-
-	it("keeps the overlay within the configured stage fraction while preserving aspect ratio", () => {
-		const layout = computeWebcamOverlayLayout({
-			stageWidth: 1280,
-			stageHeight: 720,
-			videoWidth: 1920,
-			videoHeight: 1080,
-		});
-
-		expect(layout).not.toBeNull();
-		expect(layout!.width).toBeLessThanOrEqual(Math.round(1280 * 0.18) + 1);
-		expect(layout!.height).toBeLessThanOrEqual(Math.round(720 * 0.18) + 1);
-		expect(Math.abs(layout!.width * 1080 - layout!.height * 1920)).toBeLessThanOrEqual(1920);
-	});
-
-	it("places the webcam directly below the screencast in vertical stack mode", () => {
-		const layout = computeWebcamOverlayLayout({
-			stageWidth: 1920,
-			stageHeight: 1080,
-			videoWidth: 1280,
-			videoHeight: 720,
-			screenVideoWidth: 1920,
-			screenVideoHeight: 1080,
-			layoutPreset: "vertical-stack",
-		});
-
-		expect(layout).not.toBeNull();
-		expect(layout?.y).toBe(648);
-		expect(layout?.height).toBe(432);
-		expect(layout?.width).toBe(768);
-		expect(layout?.borderRadius).toBe(0);
-	});
-
-	it("returns null for vertical stack until screen dimensions are available", () => {
-		const layout = computeWebcamOverlayLayout({
-			stageWidth: 1920,
-			stageHeight: 1080,
-			videoWidth: 1280,
-			videoHeight: 720,
-			layoutPreset: "vertical-stack",
-		});
-
-		expect(layout).toBeNull();
-	});
-});
diff --git a/src/lib/webcamOverlay.ts b/src/lib/webcamOverlay.ts
deleted file mode 100644
index b76ab6e..0000000
--- a/src/lib/webcamOverlay.ts
+++ /dev/null
@@ -1,196 +0,0 @@
-export interface WebcamOverlayLayout {
-	x: number;
-	y: number;
-	width: number;
-	height: number;
-	margin: number;
-	borderRadius: number;
-}
-
-export type WebcamLayoutPreset = "picture-in-picture" | "vertical-stack";
-
-export interface WebcamLayoutShadow {
-	color: string;
-	blur: number;
-	offsetX: number;
-	offsetY: number;
-}
-
-interface BorderRadiusRule {
-	max: number;
-	min: number;
-	fraction: number;
-}
-
-interface OverlayTransform {
-	type: "overlay";
-	maxStageFraction: number;
-	marginFraction: number;
-	minMargin: number;
-	minSize: number;
-}
-
-interface StackTransform {
-	type: "stack";
-	gap: number;
-}
-
-export interface WebcamLayoutPresetDefinition {
-	label: string;
-	transform: OverlayTransform | StackTransform;
-	borderRadius: BorderRadiusRule;
-	shadow: WebcamLayoutShadow | null;
-}
-
-const MAX_STAGE_FRACTION = 0.18;
-const MARGIN_FRACTION = 0.02;
-const MIN_SIZE = 96;
-const MAX_BORDER_RADIUS = 24;
-const WEBCAM_LAYOUT_PRESET_MAP: Record<WebcamLayoutPreset, WebcamLayoutPresetDefinition> = {
-	"picture-in-picture": {
-		label: "Picture in Picture",
-		transform: {
-			type: "overlay",
-			maxStageFraction: MAX_STAGE_FRACTION,
-			marginFraction: MARGIN_FRACTION,
-			minMargin: 12,
-			minSize: MIN_SIZE,
-		},
-		borderRadius: {
-			max: MAX_BORDER_RADIUS,
-			min: 12,
-			fraction: 0.12,
-		},
-		shadow: {
-			color: "rgba(0,0,0,0.35)",
-			blur: 24,
-			offsetX: 0,
-			offsetY: 10,
-		},
-	},
-	"vertical-stack": {
-		label: "Vertical Stack",
-		transform: {
-			type: "stack",
-			gap: 0,
-		},
-		borderRadius: {
-			max: 0,
-			min: 0,
-			fraction: 0,
-		},
-		shadow: null,
-	},
-};
-
-export const WEBCAM_LAYOUT_PRESETS = Object.entries(WEBCAM_LAYOUT_PRESET_MAP).map(
-	([value, preset]) => ({
-		value: value as WebcamLayoutPreset,
-		label: preset.label,
-	}),
-);
-
-export function getWebcamLayoutPresetDefinition(
-	preset: WebcamLayoutPreset = "picture-in-picture",
-): WebcamLayoutPresetDefinition {
-	return WEBCAM_LAYOUT_PRESET_MAP[preset];
-}
-
-export function getWebcamLayoutCssBoxShadow(
-	preset: WebcamLayoutPreset = "picture-in-picture",
-): string {
-	const shadow = getWebcamLayoutPresetDefinition(preset).shadow;
-	return shadow
-		? `${shadow.offsetX}px ${shadow.offsetY}px ${shadow.blur}px ${shadow.color}`
-		: "none";
-}
-
-export function computeWebcamOverlayLayout(params: {
-	stageWidth: number;
-	stageHeight: number;
-	videoWidth: number;
-	videoHeight: number;
-	layoutPreset?: WebcamLayoutPreset;
-	screenVideoWidth?: number;
-	screenVideoHeight?: number;
-}): WebcamOverlayLayout | null {
-	const {
-		stageWidth,
-		stageHeight,
-		videoWidth,
-		videoHeight,
-		layoutPreset = "picture-in-picture",
-		screenVideoWidth,
-		screenVideoHeight,
-	} = params;
-	const preset = getWebcamLayoutPresetDefinition(layoutPreset);
-
-	if (stageWidth <= 0 || stageHeight <= 0 || videoWidth <= 0 || videoHeight <= 0) {
-		return null;
-	}
-
-	if (preset.transform.type === "stack") {
-		if (
-			!screenVideoWidth ||
-			!screenVideoHeight ||
-			screenVideoWidth <= 0 ||
-			screenVideoHeight <= 0
-		) {
-			return null;
-		}
-
-		const gap = preset.transform.gap;
-		const scale = Math.min(
-			stageWidth / Math.max(screenVideoWidth, videoWidth),
-			stageHeight / (screenVideoHeight + gap + videoHeight),
-		);
-		const clampedScale = Number.isFinite(scale) && scale > 0 ? scale : 1;
-		const screenHeight = Math.round(screenVideoHeight * clampedScale);
-		const webcamHeight = Math.round(videoHeight * clampedScale);
-		const webcamWidth = Math.round(videoWidth * clampedScale);
-		const scaledGap = Math.round(gap * clampedScale);
-		const contentHeight = screenHeight + scaledGap + webcamHeight;
-		const topOffset = Math.max(0, Math.floor((stageHeight - contentHeight) / 2));
-
-		return {
-			x: Math.max(0, Math.floor((stageWidth - webcamWidth) / 2)),
-			y: Math.max(0, topOffset + screenHeight + scaledGap),
-			width: webcamWidth,
-			height: webcamHeight,
-			margin: 0,
-			borderRadius: Math.min(
-				preset.borderRadius.max,
-				Math.max(
-					preset.borderRadius.min,
-					Math.round(Math.min(webcamWidth, webcamHeight) * preset.borderRadius.fraction),
-				),
-			),
-		};
-	}
-
-	const transform = preset.transform;
-	const margin = Math.max(
-		transform.minMargin,
-		Math.round(Math.min(stageWidth, stageHeight) * transform.marginFraction),
-	);
-	const maxWidth = Math.max(transform.minSize, stageWidth * transform.maxStageFraction);
-	const maxHeight = Math.max(transform.minSize, stageHeight * transform.maxStageFraction);
-	const scale = Math.min(maxWidth / videoWidth, maxHeight / videoHeight);
-	const width = Math.round(videoWidth * scale);
-	const height = Math.round(videoHeight * scale);
-
-	return {
-		x: Math.max(0, Math.round(stageWidth - margin - width)),
-		y: Math.max(0, Math.round(stageHeight - margin - height)),
-		width,
-		height,
-		margin,
-		borderRadius: Math.min(
-			preset.borderRadius.max,
-			Math.max(
-				preset.borderRadius.min,
-				Math.round(Math.min(width, height) * preset.borderRadius.fraction),
-			),
-		),
-	};
-}