refactor: split constants by domain and isolate timeline panel from core

23 files changed, 569 insertions, 68 deletions

diff --git a/apps/web/src/components/editor/panels/assets/views/assets.tsx b/apps/web/src/components/editor/panels/assets/views/assets.tsx
index e17e4d4a..031d2e6a 100644
--- a/apps/web/src/components/editor/panels/assets/views/assets.tsx
+++ b/apps/web/src/components/editor/panels/assets/views/assets.tsx
@@ -25,7 +25,7 @@ import {
 	TooltipProvider,
 	TooltipTrigger,
 } from "@/components/ui/tooltip";
-import { TIMELINE_CONSTANTS } from "@/constants/timeline-constants";
+import { DEFAULT_NEW_ELEMENT_DURATION_SECONDS } from "@/lib/timeline/creation";
 import { useEditor } from "@/hooks/use-editor";
 import { useFileUpload } from "@/hooks/use-file-upload";
 import { invokeAction } from "@/lib/actions";
@@ -257,7 +257,7 @@ function MediaAssetDraggable({
 		startTime: number;
 	}) => {
 		const duration =
-			asset.duration ?? TIMELINE_CONSTANTS.DEFAULT_ELEMENT_DURATION;
+			asset.duration ?? DEFAULT_NEW_ELEMENT_DURATION_SECONDS;
 		const element = buildElementFromMedia({
 			mediaId: asset.id,
 			mediaType: asset.type,
diff --git a/apps/web/src/components/editor/panels/assets/views/settings/background.tsx b/apps/web/src/components/editor/panels/assets/views/settings/background.tsx
index 7a81188f..bbceac7d 100644
--- a/apps/web/src/components/editor/panels/assets/views/settings/background.tsx
+++ b/apps/web/src/components/editor/panels/assets/views/settings/background.tsx
@@ -8,10 +8,10 @@ import {
 	SectionTitle,

 } from "@/components/section";

 import {

-	BLUR_INTENSITY_PRESETS,

-	DEFAULT_BLUR_INTENSITY,

-	DEFAULT_COLOR,

-} from "@/constants/project-constants";

+	BACKGROUND_BLUR_INTENSITY_PRESETS,

+	DEFAULT_BACKGROUND_BLUR_INTENSITY,

+	DEFAULT_BACKGROUND_COLOR,

+} from "@/lib/background/constants";

 import { patternCraftGradients } from "@/data/colors/pattern-craft";

 import { colors } from "@/data/colors/solid";

 import { syntaxUIGradients } from "@/data/colors/syntax-ui";

@@ -164,16 +164,16 @@ export function BackgroundContent() {
 	const currentBlurIntensity = isBlurBackground

 		? (activeProject.settings.background as { blurIntensity: number })

 				.blurIntensity

-		: DEFAULT_BLUR_INTENSITY;

+		: DEFAULT_BACKGROUND_BLUR_INTENSITY;

 

 	const currentBackgroundColor = isColorBackground

 		? (activeProject.settings.background as { color: string }).color

-		: DEFAULT_COLOR;

+		: DEFAULT_BACKGROUND_COLOR;

 	const canvasSize = activeProject.settings.canvasSize;

 

 	const blurPreviews = useMemo(

 		() =>

-			BLUR_INTENSITY_PRESETS.map((blur) => (

+			BACKGROUND_BLUR_INTENSITY_PRESETS.map((blur) => (

 				<BlurPreview

 					key={blur.value}

 					blur={blur}

diff --git a/apps/web/src/components/editor/panels/assets/views/settings/index.tsx b/apps/web/src/components/editor/panels/assets/views/settings/index.tsx
index 1526a842..6c819a36 100644
--- a/apps/web/src/components/editor/panels/assets/views/settings/index.tsx
+++ b/apps/web/src/components/editor/panels/assets/views/settings/index.tsx
@@ -9,7 +9,7 @@ import {
 	SelectTrigger,
 	SelectValue,
 } from "@/components/ui/select";
-import { FPS_PRESETS } from "@/constants/project-constants";
+import { FPS_PRESETS } from "@/lib/fps/constants";
 import { useEditor } from "@/hooks/use-editor";
 import {
 	Section,
diff --git a/apps/web/src/components/editor/panels/preview/preview-viewport.tsx b/apps/web/src/components/editor/panels/preview/preview-viewport.tsx
index 8fd38768..51e5d2d0 100644
--- a/apps/web/src/components/editor/panels/preview/preview-viewport.tsx
+++ b/apps/web/src/components/editor/panels/preview/preview-viewport.tsx
@@ -17,7 +17,7 @@ import {
 	screenToCanvas,

 } from "@/lib/preview/preview-coords";

 import { clamp, isNearlyEqual } from "@/utils/math";

-import { PREVIEW_ZOOM } from "@/constants/editor-constants";

+import { PREVIEW_ZOOM } from "@/lib/preview/constants";

 

 const MIDDLE_MOUSE_BUTTON = 1;

 const IS_AT_FIT_EPSILON = 0.001;

diff --git a/apps/web/src/components/editor/panels/preview/toolbar.tsx b/apps/web/src/components/editor/panels/preview/toolbar.tsx
index 340058d0..0be1ec46 100644
--- a/apps/web/src/components/editor/panels/preview/toolbar.tsx
+++ b/apps/web/src/components/editor/panels/preview/toolbar.tsx
@@ -22,7 +22,7 @@ import {
 	SelectItem,
 	SelectSeparator,
 } from "@/components/ui/select";
-import { PREVIEW_ZOOM_PRESETS } from "@/constants/editor-constants";
+import { PREVIEW_ZOOM_PRESETS } from "@/lib/preview/constants";
 import { usePreviewViewport } from "./preview-viewport";
 import { GridPopover } from "./guide-popover";
 import { usePreviewStore } from "@/stores/preview-store";
diff --git a/apps/web/src/components/editor/panels/properties/tabs/speed-tab.tsx b/apps/web/src/components/editor/panels/properties/tabs/speed-tab.tsx
index da86c626..cb10aac3 100644
--- a/apps/web/src/components/editor/panels/properties/tabs/speed-tab.tsx
+++ b/apps/web/src/components/editor/panels/properties/tabs/speed-tab.tsx
@@ -11,7 +11,7 @@ import {
 	MAX_RETIME_RATE,

 	clampRetimeRate,

 	canMaintainPitch,

-} from "@/constants/retime-constants";

+} from "@/lib/retime/rate";

 import type { AudioElement, VideoElement } from "@/lib/timeline";

 import {

 	Section,

diff --git a/apps/web/src/components/editor/panels/properties/tabs/text-tab.tsx b/apps/web/src/components/editor/panels/properties/tabs/text-tab.tsx
index 4c58023b..11412c04 100644
--- a/apps/web/src/components/editor/panels/properties/tabs/text-tab.tsx
+++ b/apps/web/src/components/editor/panels/properties/tabs/text-tab.tsx
@@ -18,13 +18,13 @@ import { Button } from "@/components/ui/button";
 import { uppercase } from "@/utils/string";
 import { clamp, formatNumberForDisplay } from "@/utils/math";
 import { useEditor } from "@/hooks/use-editor";
-import { DEFAULT_COLOR } from "@/constants/project-constants";
 import {
 	CORNER_RADIUS_MAX,
+	DEFAULT_TEXT_COLOR,
 	CORNER_RADIUS_MIN,
 	MAX_FONT_SIZE,
 	MIN_FONT_SIZE,
-} from "@/constants/text-constants";
+} from "@/lib/text/constants";
 import { usePropertyDraft } from "../hooks/use-property-draft";
 import { useKeyframedColorProperty } from "../hooks/use-keyframed-color-property";
 import { useKeyframedNumberProperty } from "../hooks/use-keyframed-number-property";
@@ -343,7 +343,7 @@ function BackgroundSection({
 	trackId: string;
 }) {
 	const editor = useEditor();
-	const lastSelectedColor = useRef(DEFAULT_COLOR);
+	const lastSelectedColor = useRef(DEFAULT_TEXT_COLOR);
 	const { localTime, isPlayheadWithinElementRange } = useElementPlayhead({
 		startTime: element.startTime,
 		duration: element.duration,
diff --git a/apps/web/src/components/editor/panels/timeline/bookmarks.tsx b/apps/web/src/components/editor/panels/timeline/bookmarks.tsx
index e2dc09f1..d4b1657e 100644
--- a/apps/web/src/components/editor/panels/timeline/bookmarks.tsx
+++ b/apps/web/src/components/editor/panels/timeline/bookmarks.tsx
@@ -6,10 +6,10 @@ import { useEditor } from "@/hooks/use-editor";
 import type { BookmarkDragState } from "@/hooks/timeline/use-bookmark-drag";
 import { BOOKMARK_TIME_EPSILON } from "@/lib/timeline/bookmarks";
 import {
-	DEFAULT_BOOKMARK_COLOR,
-	TIMELINE_BOOKMARK_ROW_HEIGHT,
-} from "@/constants/timeline-constants";
-import { DEFAULT_FPS } from "@/constants/project-constants";
+	DEFAULT_TIMELINE_BOOKMARK_COLOR,
+} from "./theme";
+import { TIMELINE_BOOKMARK_ROW_HEIGHT_PX } from "./layout";
+import { DEFAULT_FPS } from "@/lib/fps/constants";
 import { getSnappedSeekTime } from "opencut-wasm";
 import {
 	ArrowTurnBackwardIcon,
@@ -83,12 +83,12 @@ export function TimelineBookmarksRow({
 	return (
 		<div
 			className="relative flex-1 overflow-hidden"
-			style={{ height: TIMELINE_BOOKMARK_ROW_HEIGHT }}
+			style={{ height: TIMELINE_BOOKMARK_ROW_HEIGHT_PX }}
 		>
 			<button
 				className="relative w-full cursor-default select-none border-0 bg-transparent p-0"
 				style={{
-					height: TIMELINE_BOOKMARK_ROW_HEIGHT,
+					height: TIMELINE_BOOKMARK_ROW_HEIGHT_PX,
 					width: `${dynamicTimelineWidth}px`,
 				}}
 				aria-label="Timeline ruler"
@@ -153,7 +153,7 @@ function TimelineBookmark({
 	const left = timelineTimeToSnappedPixels({ time: displayTime, zoomLevel });
 	const bookmarkLeft = left - BOOKMARK_HALF_WIDTH_PX;
 	const rightHalfLeft = BOOKMARK_HALF_WIDTH_PX + Math.max(durationWidth, 0);
-	const iconColor = bookmark.color ?? DEFAULT_BOOKMARK_COLOR;
+	const iconColor = bookmark.color ?? DEFAULT_TIMELINE_BOOKMARK_COLOR;
 
 	const handleSeek = () => seekToBookmarkTime({ editor, time });
 
@@ -298,12 +298,16 @@ function BookmarkPopoverContent({
 }) {
 	const editor = useEditor();
 	const [draftColorHex, setDraftColorHex] = useState(
-		(bookmark.color ?? DEFAULT_BOOKMARK_COLOR).replace("#", "").toUpperCase(),
+		(bookmark.color ?? DEFAULT_TIMELINE_BOOKMARK_COLOR)
+			.replace("#", "")
+			.toUpperCase(),
 	);
 
 	useEffect(() => {
 		setDraftColorHex(
-			(bookmark.color ?? DEFAULT_BOOKMARK_COLOR).replace("#", "").toUpperCase(),
+			(bookmark.color ?? DEFAULT_TIMELINE_BOOKMARK_COLOR)
+				.replace("#", "")
+				.toUpperCase(),
 		);
 	}, [bookmark.color]);
 
@@ -357,7 +361,7 @@ function BookmarkPopoverContent({
 					/>
 					{bookmark.color &&
 						bookmark.color.replace(/^#/, "").toUpperCase() !==
-							DEFAULT_BOOKMARK_COLOR.replace(/^#/, "").toUpperCase() && (
+							DEFAULT_TIMELINE_BOOKMARK_COLOR.replace(/^#/, "").toUpperCase() && (
 							<Button
 								type="button"
 								variant="text"
diff --git a/apps/web/src/components/editor/panels/timeline/drag-line.tsx b/apps/web/src/components/editor/panels/timeline/drag-line.tsx
index a5a145b4..89a4c93f 100644
--- a/apps/web/src/components/editor/panels/timeline/drag-line.tsx
+++ b/apps/web/src/components/editor/panels/timeline/drag-line.tsx
@@ -1,6 +1,6 @@
-import { getDropLineY } from "@/lib/timeline/drop-utils";

+import { getDropLineY } from "./drop-target";

 import type { TimelineTrack, DropTarget } from "@/lib/timeline";

-import { TIMELINE_LAYERS } from "@/constants/timeline-constants";

+import { TIMELINE_LAYERS } from "./layers";

 

 interface DragLineProps {

 	dropTarget: DropTarget | null;

diff --git a/apps/web/src/components/editor/panels/timeline/drop-target.ts b/apps/web/src/components/editor/panels/timeline/drop-target.ts
new file mode 100644
index 00000000..dbd4efaf
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/drop-target.ts
@@ -0,0 +1,251 @@
+import type { TimelineTrack, TimelineElement } from "@/lib/timeline";
+import type { ComputeDropTargetParams, DropTarget } from "@/lib/timeline";
+import { resolveTrackPlacement } from "@/lib/timeline/placement";
+import { TIMELINE_TRACK_GAP_PX } from "./layout";
+import { getTrackHeight } from "./track-layout";
+
+function findElementAtPosition({
+	mouseX,
+	tracks,
+	trackIndex,
+	targetElementTypes,
+	pixelsPerSecond,
+	zoomLevel,
+}: {
+	mouseX: number;
+	tracks: TimelineTrack[];
+	trackIndex: number;
+	targetElementTypes: string[];
+	pixelsPerSecond: number;
+	zoomLevel: number;
+}): { elementId: string; trackId: string } | null {
+	const time = mouseX / (pixelsPerSecond * zoomLevel);
+	const track = tracks[trackIndex];
+	if (!track || !("elements" in track)) return null;
+
+	const hit = track.elements.find(
+		(element: TimelineElement) =>
+			targetElementTypes.includes(element.type) &&
+			element.startTime <= time &&
+			time < element.startTime + element.duration,
+	);
+	if (!hit) return null;
+	return { elementId: hit.id, trackId: track.id };
+}
+
+function getTrackAtY({
+	mouseY,
+	tracks,
+	verticalDragDirection,
+}: {
+	mouseY: number;
+	tracks: TimelineTrack[];
+	verticalDragDirection?: "up" | "down" | null;
+}): { trackIndex: number; relativeY: number } | null {
+	let cumulativeHeight = 0;
+
+	for (let i = 0; i < tracks.length; i++) {
+		const trackHeight = getTrackHeight({ type: tracks[i].type });
+		const trackTop = cumulativeHeight;
+		const trackBottom = trackTop + trackHeight;
+
+		if (mouseY >= trackTop && mouseY < trackBottom) {
+			return {
+				trackIndex: i,
+				relativeY: mouseY - trackTop,
+			};
+		}
+
+		if (i < tracks.length - 1 && verticalDragDirection) {
+			const gapTop = trackBottom;
+			const gapBottom = gapTop + TIMELINE_TRACK_GAP_PX;
+			if (mouseY >= gapTop && mouseY < gapBottom) {
+				const isDraggingUp = verticalDragDirection === "up";
+				return {
+					trackIndex: isDraggingUp ? i : i + 1,
+					relativeY: isDraggingUp ? trackHeight - 1 : 0,
+				};
+			}
+		}
+
+		cumulativeHeight += trackHeight + TIMELINE_TRACK_GAP_PX;
+	}
+
+	return null;
+}
+
+const EMPTY_TARGET_ELEMENT = null;
+
+function fallbackNewTrackDropTarget({
+	xPosition,
+}: {
+	xPosition: number;
+}): DropTarget {
+	return {
+		trackIndex: 0,
+		isNewTrack: true,
+		insertPosition: null,
+		xPosition,
+		targetElement: EMPTY_TARGET_ELEMENT,
+	};
+}
+
+export function computeDropTarget({
+	elementType,
+	mouseX,
+	mouseY,
+	tracks,
+	playheadTime,
+	isExternalDrop,
+	elementDuration,
+	pixelsPerSecond,
+	zoomLevel,
+	verticalDragDirection,
+	startTimeOverride,
+	excludeElementId,
+	targetElementTypes,
+}: ComputeDropTargetParams): DropTarget {
+	const xPosition =
+		typeof startTimeOverride === "number"
+			? startTimeOverride
+			: isExternalDrop
+				? playheadTime
+				: Math.max(0, mouseX / (pixelsPerSecond * zoomLevel));
+
+	if (tracks.length === 0) {
+		const placementResult = resolveTrackPlacement({
+			tracks,
+			elementType,
+			timeSpans: [{ startTime: xPosition, duration: elementDuration, excludeElementId }],
+			strategy: {
+				type: "preferIndex",
+				trackIndex: 0,
+				hoverDirection: "below",
+				createNewTrackOnly: true,
+			},
+		});
+		const emptyTimelineResult =
+			placementResult?.kind === "newTrack" ? placementResult : null;
+		if (!emptyTimelineResult) {
+			return fallbackNewTrackDropTarget({ xPosition });
+		}
+
+		return {
+			trackIndex: emptyTimelineResult.insertIndex,
+			isNewTrack: true,
+			insertPosition: emptyTimelineResult.insertPosition,
+			xPosition,
+			targetElement: EMPTY_TARGET_ELEMENT,
+		};
+	}
+
+	const trackAtMouse = getTrackAtY({ mouseY, tracks, verticalDragDirection });
+
+	if (!trackAtMouse) {
+		const isAboveAllTracks = mouseY < 0;
+
+		const placementResult = resolveTrackPlacement({
+			tracks,
+			elementType,
+			timeSpans: [{ startTime: xPosition, duration: elementDuration, excludeElementId }],
+			strategy: {
+				type: "preferIndex",
+				trackIndex: isAboveAllTracks ? 0 : tracks.length - 1,
+				hoverDirection: isAboveAllTracks ? "above" : "below",
+				createNewTrackOnly: true,
+			},
+		});
+		const outOfBoundsResult =
+			placementResult?.kind === "newTrack" ? placementResult : null;
+		if (!outOfBoundsResult) {
+			return fallbackNewTrackDropTarget({ xPosition });
+		}
+
+		return {
+			trackIndex: outOfBoundsResult.insertIndex,
+			isNewTrack: true,
+			insertPosition: outOfBoundsResult.insertPosition,
+			xPosition,
+			targetElement: EMPTY_TARGET_ELEMENT,
+		};
+	}
+
+	const { trackIndex, relativeY } = trackAtMouse;
+	const track = tracks[trackIndex];
+
+	if (targetElementTypes && targetElementTypes.length > 0) {
+		const targetElement = findElementAtPosition({
+			mouseX,
+			tracks,
+			trackIndex,
+			targetElementTypes,
+			pixelsPerSecond,
+			zoomLevel,
+		});
+		if (targetElement) {
+			return {
+				trackIndex,
+				isNewTrack: false,
+				insertPosition: null,
+				xPosition,
+				targetElement,
+			};
+		}
+	}
+
+	const trackHeight = getTrackHeight({ type: track.type });
+	const placementResult = resolveTrackPlacement({
+		tracks,
+		elementType,
+		timeSpans: [{ startTime: xPosition, duration: elementDuration, excludeElementId }],
+		strategy: {
+			type: "preferIndex",
+			trackIndex,
+			hoverDirection: relativeY < trackHeight / 2 ? "above" : "below",
+			verticalDragDirection,
+		},
+	});
+	if (!placementResult) {
+		return fallbackNewTrackDropTarget({ xPosition });
+	}
+
+	if (placementResult.kind === "existingTrack") {
+		const adjustedXPosition = placementResult.adjustedStartTime ?? xPosition;
+
+		return {
+			trackIndex: placementResult.trackIndex,
+			isNewTrack: false,
+			insertPosition: null,
+			xPosition: adjustedXPosition,
+			targetElement: EMPTY_TARGET_ELEMENT,
+		};
+	}
+
+	return {
+		trackIndex: placementResult.insertIndex,
+		isNewTrack: true,
+		insertPosition: placementResult.insertPosition,
+		xPosition,
+		targetElement: EMPTY_TARGET_ELEMENT,
+	};
+}
+
+export function getDropLineY({
+	dropTarget,
+	tracks,
+}: {
+	dropTarget: DropTarget;
+	tracks: TimelineTrack[];
+}): number {
+	const safeTrackIndex = Math.min(
+		Math.max(dropTarget.trackIndex, 0),
+		tracks.length,
+	);
+	let y = 0;
+
+	for (let i = 0; i < safeTrackIndex; i++) {
+		y += getTrackHeight({ type: tracks[i].type }) + TIMELINE_TRACK_GAP_PX;
+	}
+
+	return y;
+}
diff --git a/apps/web/src/components/editor/panels/timeline/index.tsx b/apps/web/src/components/editor/panels/timeline/index.tsx
index 819413e6..4114ae2c 100644
--- a/apps/web/src/components/editor/panels/timeline/index.tsx
+++ b/apps/web/src/components/editor/panels/timeline/index.tsx
@@ -38,20 +38,26 @@ import { SnapIndicator } from "./snap-indicator";
 import type { SnapPoint } from "@/lib/timeline/snap-utils";
 import type { TimelineTrack } from "@/lib/timeline";
 import {
-	TIMELINE_CONSTANTS,
-	TRACK_GAP,
 	TIMELINE_SCROLLBAR_SIZE_PX,
-} from "@/constants/timeline-constants";
+	TIMELINE_CONTENT_TOP_PADDING_PX,
+	TIMELINE_TRACK_GAP_PX,
+	TIMELINE_TRACK_LABELS_COLUMN_WIDTH_PX,
+} from "./layout";
 import { useElementInteraction } from "@/hooks/timeline/element/use-element-interaction";
 import {
-	getTrackHeight,
-	getCumulativeHeightBefore,
-	getTotalTracksHeight,
-	canTracktHaveAudio,
+	canTrackHaveAudio,
 	canTrackBeHidden,
 	getTimelineZoomMin,
 	getTimelinePaddingPx,
 } from "@/lib/timeline";
+import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/lib/timeline/scale";
+import {
+	getTrackHeight,
+	getCumulativeHeightBefore,
+	getTotalTracksHeight,
+} from "./track-layout";
+import { SELECTED_TRACK_ROW_CLASS } from "./theme";
+import { TIMELINE_HORIZONTAL_WHEEL_STEP_PX } from "./interaction";
 import { isMainTrack } from "@/lib/timeline/placement";
 import { TimelineToolbar } from "./timeline-toolbar";
 import { useElementSelection } from "@/hooks/timeline/element/use-element-selection";
@@ -67,7 +73,7 @@ import { useEditor } from "@/hooks/use-editor";
 import { useTimelinePlayhead } from "@/hooks/timeline/use-timeline-playhead";
 import { DragLine } from "./drag-line";
 import { invokeAction } from "@/lib/actions";
-import { resolveTimelineElementIntersections } from "@/lib/timeline/selection-hit-testing";
+import { resolveTimelineElementIntersections } from "./selection-hit-testing";
 import { cn } from "@/utils/ui";
 
 const TRACKS_CONTAINER_MAX_HEIGHT = 800;
@@ -230,7 +236,7 @@ export function Timeline() {
 					Math.abs(e.deltaX) > Math.abs(e.deltaY) ? e.deltaX : e.deltaY;
 				const clamped =
 					Math.sign(raw) *
-					Math.min(Math.abs(raw), TIMELINE_CONSTANTS.HORIZONTAL_WHEEL_STEP_PX);
+					Math.min(Math.abs(raw), TIMELINE_HORIZONTAL_WHEEL_STEP_PX);
 				tracks.scrollLeft = Math.max(0, tracks.scrollLeft + clamped);
 			} else {
 				tracks.scrollTop = Math.max(0, tracks.scrollTop + e.deltaY);
@@ -335,7 +341,7 @@ export function Timeline() {
 	const containerWidth =
 		tracksContainerRef.current?.clientWidth || FALLBACK_CONTAINER_WIDTH;
 	const contentWidth =
-		timelineDuration * TIMELINE_CONSTANTS.PIXELS_PER_SECOND * zoomLevel;
+		timelineDuration * BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel;
 	const paddingPx = getTimelinePaddingPx({
 		containerWidth,
 		zoomLevel,
@@ -383,7 +389,7 @@ export function Timeline() {
 
 	const timelineHeaderHeight =
 		(timelineHeaderRef.current?.getBoundingClientRect().height ?? 0) +
-			TIMELINE_CONSTANTS.PADDING_TOP_PX || 0;
+			TIMELINE_CONTENT_TOP_PADDING_PX || 0;
 
 	return (
 		<section
@@ -483,7 +489,7 @@ export function Timeline() {
 												TRACKS_CONTAINER_HEIGHT.max,
 												getTotalTracksHeight({ tracks }),
 											),
-										) + TIMELINE_CONSTANTS.PADDING_TOP_PX
+										) + TIMELINE_CONTENT_TOP_PADDING_PX
 									}px`,
 								}}
 								onMouseDown={(event) => {
@@ -577,7 +583,10 @@ function TrackLabelsPanel({
 	);
 
 	return (
-		<div className="flex w-28 shrink-0 flex-col border-r">
+		<div
+			className="flex shrink-0 flex-col border-r"
+			style={{ width: `${TIMELINE_TRACK_LABELS_COLUMN_WIDTH_PX}px` }}
+		>
 			<div
 				className="shrink-0"
 				style={{ height: timelineHeaderHeight || 48 }}
@@ -585,21 +594,24 @@ function TrackLabelsPanel({
 			<div ref={trackLabelsRef} className="flex-1 overflow-hidden">
 				<div ref={trackLabelsScrollRef} className="size-full overflow-hidden">
 					{tracks.length > 0 && (
-						<div className="flex flex-col" style={{ gap: `${TRACK_GAP}px` }}>
+						<div
+							className="flex flex-col"
+							style={{ gap: `${TIMELINE_TRACK_GAP_PX}px` }}
+						>
 							{tracks.map((track) => (
 								<div
 									key={track.id}
 									className={cn(
 										"group flex items-center px-3",
 										tracksWithSelection.has(track.id) &&
-											TIMELINE_CONSTANTS.TRACK_SELECTED_BG,
+											SELECTED_TRACK_ROW_CLASS,
 									)}
 									style={{
 										height: `${getTrackHeight({ type: track.type })}px`,
 									}}
 								>
 									<div className="flex min-w-0 flex-1 items-center justify-end gap-2">
-										{canTracktHaveAudio(track) && (
+										{canTrackHaveAudio(track) && (
 											<TrackToggleIcon
 												isOff={track.muted}
 												icons={{ on: VolumeHighIcon, off: VolumeOffIcon }}
@@ -707,10 +719,10 @@ function TimelineTrackRows({
 							className={cn(
 								"absolute right-0 left-0 transition-colors",
 								tracksWithSelection.has(track.id) &&
-									TIMELINE_CONSTANTS.TRACK_SELECTED_BG,
+									SELECTED_TRACK_ROW_CLASS,
 							)}
 							style={{
-								top: `${TIMELINE_CONSTANTS.PADDING_TOP_PX + getCumulativeHeightBefore({ tracks, trackIndex: index })}px`,
+								top: `${TIMELINE_CONTENT_TOP_PADDING_PX + getCumulativeHeightBefore({ tracks, trackIndex: index })}px`,
 								height: `${getTrackHeight({ type: track.type })}px`,
 							}}
 						>
@@ -753,7 +765,7 @@ function TimelineTrackRows({
 								timeline.toggleTrackMute({ trackId: track.id });
 							}}
 						>
-							{canTracktHaveAudio(track) && track.muted
+							{canTrackHaveAudio(track) && track.muted
 								? "Unmute track"
 								: "Mute track"}
 						</ContextMenuItem>
diff --git a/apps/web/src/components/editor/panels/timeline/interaction.ts b/apps/web/src/components/editor/panels/timeline/interaction.ts
new file mode 100644
index 00000000..fe0210a4
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/interaction.ts
@@ -0,0 +1,4 @@
+export const TIMELINE_DRAG_THRESHOLD_PX = 5;
+export const TIMELINE_HORIZONTAL_WHEEL_STEP_PX = 40;
+export const TIMELINE_ZOOM_BUTTON_FACTOR = 1.7;
+export const TIMELINE_ZOOM_ANCHOR_PLAYHEAD_THRESHOLD = 0.15;
diff --git a/apps/web/src/components/editor/panels/timeline/layers.ts b/apps/web/src/components/editor/panels/timeline/layers.ts
new file mode 100644
index 00000000..d59db412
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/layers.ts
@@ -0,0 +1,6 @@
+export const TIMELINE_LAYERS = {
+	trackContent: 10,
+	dragLine: 20,
+	playhead: 30,
+	snapIndicator: 40,
+} as const;
diff --git a/apps/web/src/components/editor/panels/timeline/layout.ts b/apps/web/src/components/editor/panels/timeline/layout.ts
new file mode 100644
index 00000000..88443797
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/layout.ts
@@ -0,0 +1,16 @@
+import type { TrackType } from "@/lib/timeline";
+
+export const TIMELINE_TRACK_HEIGHTS_PX: Record<TrackType, number> = {
+	video: 65,
+	text: 25,
+	audio: 50,
+	graphic: 25,
+	effect: 25,
+} as const;
+
+export const TIMELINE_TRACK_GAP_PX = 6;
+export const TIMELINE_TRACK_LABELS_COLUMN_WIDTH_PX = 112;
+export const TIMELINE_RULER_HEIGHT_PX = 22;
+export const TIMELINE_BOOKMARK_ROW_HEIGHT_PX = 16;
+export const TIMELINE_SCROLLBAR_SIZE_PX = 12;
+export const TIMELINE_CONTENT_TOP_PADDING_PX = 2;
diff --git a/apps/web/src/components/editor/panels/timeline/selection-hit-testing.ts b/apps/web/src/components/editor/panels/timeline/selection-hit-testing.ts
new file mode 100644
index 00000000..6488e29a
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/selection-hit-testing.ts
@@ -0,0 +1,136 @@
+import type { TimelineTrack } from "@/lib/timeline";
+import { getTimelinePixelsPerSecond } from "@/lib/timeline/pixel-utils";
+import {
+	TIMELINE_CONTENT_TOP_PADDING_PX,
+} from "./layout";
+import { getCumulativeHeightBefore, getTrackHeight } from "./track-layout";
+
+type TimelineElementRef = { trackId: string; elementId: string };
+
+interface SelectionRectangle {
+	left: number;
+	top: number;
+	right: number;
+	bottom: number;
+}
+
+function getNormalizedRectangle({
+	startPos,
+	endPos,
+}: {
+	startPos: { x: number; y: number };
+	endPos: { x: number; y: number };
+}): SelectionRectangle {
+	return {
+		left: Math.min(startPos.x, endPos.x),
+		top: Math.min(startPos.y, endPos.y),
+		right: Math.max(startPos.x, endPos.x),
+		bottom: Math.max(startPos.y, endPos.y),
+	};
+}
+
+function getSelectionRectangleInContent({
+	container,
+	scrollContainer,
+	startPos,
+	endPos,
+}: {
+	container: HTMLElement;
+	scrollContainer: HTMLDivElement | null;
+	startPos: { x: number; y: number };
+	endPos: { x: number; y: number };
+}): SelectionRectangle {
+	const containerRect = container.getBoundingClientRect();
+	const scrollRect = scrollContainer?.getBoundingClientRect() ?? containerRect;
+	const scrollLeft = scrollContainer?.scrollLeft ?? 0;
+	const scrollTop = scrollContainer?.scrollTop ?? 0;
+
+	const adjustedStart = {
+		x: startPos.x - containerRect.left + scrollLeft,
+		y: startPos.y - scrollRect.top + scrollTop,
+	};
+	const adjustedEnd = {
+		x: endPos.x - containerRect.left + scrollLeft,
+		y: endPos.y - scrollRect.top + scrollTop,
+	};
+
+	return getNormalizedRectangle({
+		startPos: adjustedStart,
+		endPos: adjustedEnd,
+	});
+}
+
+function isRectangleIntersecting({
+	elementRectangle,
+	selectionRectangle,
+}: {
+	elementRectangle: SelectionRectangle;
+	selectionRectangle: SelectionRectangle;
+}): boolean {
+	return !(
+		elementRectangle.right < selectionRectangle.left ||
+		elementRectangle.left > selectionRectangle.right ||
+		elementRectangle.bottom < selectionRectangle.top ||
+		elementRectangle.top > selectionRectangle.bottom
+	);
+}
+
+export function resolveTimelineElementIntersections({
+	container,
+	scrollContainer,
+	tracks,
+	zoomLevel,
+	startPos,
+	currentPos,
+}: {
+	container: HTMLElement;
+	scrollContainer: HTMLDivElement | null;
+	tracks: TimelineTrack[];
+	zoomLevel: number;
+	startPos: { x: number; y: number };
+	currentPos: { x: number; y: number };
+}): TimelineElementRef[] {
+	const selectionRectangle = getSelectionRectangleInContent({
+		container,
+		scrollContainer,
+		startPos,
+		endPos: currentPos,
+	});
+	const pixelsPerSecond = getTimelinePixelsPerSecond({ zoomLevel });
+	const selectedElements: TimelineElementRef[] = [];
+
+	for (const [trackIndex, track] of tracks.entries()) {
+		const trackTop = getCumulativeHeightBefore({
+			tracks,
+			trackIndex,
+		});
+		const trackHeight = getTrackHeight({ type: track.type });
+		const elementTop = TIMELINE_CONTENT_TOP_PADDING_PX + trackTop;
+		const elementBottom = elementTop + trackHeight;
+
+		for (const element of track.elements) {
+			const elementLeft = element.startTime * pixelsPerSecond;
+			const elementRight = elementLeft + element.duration * pixelsPerSecond;
+			const elementRectangle = {
+				left: elementLeft,
+				top: elementTop,
+				right: elementRight,
+				bottom: elementBottom,
+			};
+
+			if (
+				isRectangleIntersecting({
+					elementRectangle,
+					selectionRectangle,
+				})
+			) {
+				selectedElements.push({
+					trackId: track.id,
+					elementId: element.id,
+				});
+			}
+		}
+	}
+
+	return selectedElements;
+}
diff --git a/apps/web/src/components/editor/panels/timeline/snap-indicator.tsx b/apps/web/src/components/editor/panels/timeline/snap-indicator.tsx
index 766d0843..a86e2a5e 100644
--- a/apps/web/src/components/editor/panels/timeline/snap-indicator.tsx
+++ b/apps/web/src/components/editor/panels/timeline/snap-indicator.tsx
@@ -6,7 +6,7 @@ import {
 	getCenteredLineLeft,

 	TIMELINE_INDICATOR_LINE_WIDTH_PX,

 } from "@/lib/timeline";

-import { TIMELINE_LAYERS } from "@/constants/timeline-constants";

+import { TIMELINE_LAYERS } from "./layers";

 interface SnapIndicatorProps {

 	snapPoint: SnapPoint | null;

 	zoomLevel: number;

diff --git a/apps/web/src/components/editor/panels/timeline/theme.ts b/apps/web/src/components/editor/panels/timeline/theme.ts
new file mode 100644
index 00000000..e7fc1f11
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/theme.ts
@@ -0,0 +1,29 @@
+import type { TrackType } from "@/lib/timeline";
+
+export const TIMELINE_TRACK_THEME: Record<
+	TrackType,
+	{
+		elementClassName: string;
+		waveformColor?: string;
+	}
+> = {
+	video: { elementClassName: "transparent" },
+	text: { elementClassName: "bg-[#5DBAA0]" },
+	audio: {
+		elementClassName: "bg-[#8F5DBA]",
+		waveformColor: "rgba(255, 255, 255, 0.5)",
+	},
+	graphic: { elementClassName: "bg-[#BA5D7A]" },
+	effect: { elementClassName: "bg-[#5d93ba]" },
+} as const;
+
+export const SELECTED_TRACK_ROW_CLASS = "bg-accent/50";
+export const DEFAULT_TIMELINE_BOOKMARK_COLOR = "#009dff";
+
+export function getTimelineElementClassName({
+	type,
+}: {
+	type: TrackType;
+}): string {
+	return TIMELINE_TRACK_THEME[type].elementClassName.trim();
+}
diff --git a/apps/web/src/components/editor/panels/timeline/timeline-element.tsx b/apps/web/src/components/editor/panels/timeline/timeline-element.tsx
index bb30b0b0..25218d78 100644
--- a/apps/web/src/components/editor/panels/timeline/timeline-element.tsx
+++ b/apps/web/src/components/editor/panels/timeline/timeline-element.tsx
@@ -12,8 +12,6 @@ import { useKeyframeSelection } from "@/hooks/timeline/element/use-keyframe-sele
 import type { SnapPoint } from "@/lib/timeline/snap-utils";

 import { getElementKeyframes } from "@/lib/animation";

 import {

-	getElementClasses,

-	getTrackHeight,

 	canElementHaveAudio,

 	canElementBeHidden,

 	hasElementEffects,

@@ -21,7 +19,11 @@ import {
 	timelineTimeToPixels,

 	timelineTimeToSnappedPixels,

 } from "@/lib/timeline";

-import { ELEMENT_TYPE_CONFIG } from "@/constants/timeline-constants";

+import { getTrackHeight } from "./track-layout";

+import {

+	getTimelineElementClassName,

+	TIMELINE_TRACK_THEME,

+} from "./theme";

 import {

 	ContextMenu,

 	ContextMenuContent,

@@ -464,7 +466,7 @@ function ElementInner({
 				<div

 					className={cn(

 						"absolute inset-0 overflow-hidden rounded-sm",

-						getElementClasses({ type: track.type }),

+						getTimelineElementClassName({ type: track.type }),

 						isReducedOpacity && "opacity-50",

 					)}

 				>

@@ -710,7 +712,7 @@ function AudioElementContent({ element }: { element: AudioElement }) {
 				<AudioWaveform

 					audioBuffer={audioBuffer}

 					audioUrl={audioUrl}

-					color={ELEMENT_TYPE_CONFIG.audio.waveformColor}

+					color={TIMELINE_TRACK_THEME.audio.waveformColor}

 				/>

 				<MediaElementHeader name={mediaLabel} hasFade={false} />

 			</div>

diff --git a/apps/web/src/components/editor/panels/timeline/timeline-playhead.tsx b/apps/web/src/components/editor/panels/timeline/timeline-playhead.tsx
index 1abe65bd..361f1398 100644
--- a/apps/web/src/components/editor/panels/timeline/timeline-playhead.tsx
+++ b/apps/web/src/components/editor/panels/timeline/timeline-playhead.tsx
@@ -9,9 +9,9 @@ import {
 import { useTimelinePlayhead } from "@/hooks/timeline/use-timeline-playhead";
 import { useEditor } from "@/hooks/use-editor";
 import {
-	TIMELINE_LAYERS,
 	TIMELINE_SCROLLBAR_SIZE_PX,
-} from "@/constants/timeline-constants";
+} from "./layout";
+import { TIMELINE_LAYERS } from "./layers";
 
 interface TimelinePlayheadProps {
 	zoomLevel: number;
diff --git a/apps/web/src/components/editor/panels/timeline/timeline-ruler.tsx b/apps/web/src/components/editor/panels/timeline/timeline-ruler.tsx
index 09562f23..9e49bf6c 100644
--- a/apps/web/src/components/editor/panels/timeline/timeline-ruler.tsx
+++ b/apps/web/src/components/editor/panels/timeline/timeline-ruler.tsx
@@ -1,9 +1,9 @@
 import { type JSX, useLayoutEffect, useRef } from "react";
 import {
-	TIMELINE_CONSTANTS,
-	TIMELINE_RULER_HEIGHT,
-} from "@/constants/timeline-constants";
-import { DEFAULT_FPS } from "@/constants/project-constants";
+	BASE_TIMELINE_PIXELS_PER_SECOND,
+} from "@/lib/timeline/scale";
+import { TIMELINE_RULER_HEIGHT_PX } from "./layout";
+import { DEFAULT_FPS } from "@/lib/fps/constants";
 import { useEditor } from "@/hooks/use-editor";
 import { getRulerConfig, shouldShowLabel } from "@/lib/timeline/ruler-utils";
 import { useScrollPosition } from "@/hooks/timeline/use-scroll-position";
@@ -31,7 +31,7 @@ export function TimelineRuler({
 	handleRulerMouseDown,
 }: TimelineRulerProps) {
 	const duration = useEditor((e) => e.timeline.getTotalDuration());
-	const pixelsPerSecond = TIMELINE_CONSTANTS.PIXELS_PER_SECOND * zoomLevel;
+	const pixelsPerSecond = BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel;
 	const visibleDuration = dynamicTimelineWidth / pixelsPerSecond;
 	const effectiveDuration = Math.max(duration, visibleDuration);
 	const fps =
@@ -107,7 +107,7 @@ export function TimelineRuler({
 			aria-valuemax={effectiveDuration}
 			aria-valuenow={0}
 			className="relative flex-1 overflow-x-visible"
-			style={{ height: TIMELINE_RULER_HEIGHT }}
+			style={{ height: TIMELINE_RULER_HEIGHT_PX }}
 			onWheel={handleWheel}
 			onClick={(event) => {
 				// Ruler seek already happens on mousedown via playhead scrubbing.
@@ -124,7 +124,7 @@ export function TimelineRuler({
 				ref={rulerRef}
 				className="relative cursor-default select-none"
 				style={{
-					height: TIMELINE_RULER_HEIGHT,
+					height: TIMELINE_RULER_HEIGHT_PX,
 					width: `${dynamicTimelineWidth}px`,
 				}}
 				onMouseDown={handleRulerMouseDown}
diff --git a/apps/web/src/components/editor/panels/timeline/timeline-toolbar.tsx b/apps/web/src/components/editor/panels/timeline/timeline-toolbar.tsx
index ff43e00a..ecaf37e2 100644
--- a/apps/web/src/components/editor/panels/timeline/timeline-toolbar.tsx
+++ b/apps/web/src/components/editor/panels/timeline/timeline-toolbar.tsx
@@ -14,7 +14,10 @@ import {
 	SplitButtonSeparator,
 } from "@/components/ui/split-button";
 import { Slider } from "@/components/ui/slider";
-import { TIMELINE_CONSTANTS } from "@/constants/timeline-constants";
+import {
+	TIMELINE_ZOOM_BUTTON_FACTOR,
+} from "./interaction";
+import { TIMELINE_ZOOM_MAX } from "@/lib/timeline/scale";
 import { sliderToZoom, zoomToSlider } from "@/lib/timeline/zoom-utils";
 import { ScenesView } from "@/components/editor/scenes-view";
 import { type TActionWithOptionalArgs, invokeAction } from "@/lib/actions";
@@ -60,10 +63,10 @@ export function TimelineToolbar({
 		const newZoomLevel =
 			direction === "in"
 				? Math.min(
-						TIMELINE_CONSTANTS.ZOOM_MAX,
-						zoomLevel * TIMELINE_CONSTANTS.ZOOM_BUTTON_FACTOR,
+						TIMELINE_ZOOM_MAX,
+						zoomLevel * TIMELINE_ZOOM_BUTTON_FACTOR,
 					)
-				: Math.max(minZoom, zoomLevel / TIMELINE_CONSTANTS.ZOOM_BUTTON_FACTOR);
+				: Math.max(minZoom, zoomLevel / TIMELINE_ZOOM_BUTTON_FACTOR);
 		setZoomLevel({ zoom: newZoomLevel });
 	};
 
diff --git a/apps/web/src/components/editor/panels/timeline/timeline-track.tsx b/apps/web/src/components/editor/panels/timeline/timeline-track.tsx
index ffc2007b..888e1496 100644
--- a/apps/web/src/components/editor/panels/timeline/timeline-track.tsx
+++ b/apps/web/src/components/editor/panels/timeline/timeline-track.tsx
@@ -5,7 +5,8 @@ import { TimelineElement } from "./timeline-element";
 import type { TimelineTrack } from "@/lib/timeline";

 import type { TimelineElement as TimelineElementType } from "@/lib/timeline";

 import type { SnapPoint } from "@/lib/timeline/snap-utils";

-import { TIMELINE_CONSTANTS, TIMELINE_LAYERS } from "@/constants/timeline-constants";

+import { TIMELINE_LAYERS } from "./layers";

+import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/lib/timeline/scale";

 import { useEdgeAutoScroll } from "@/hooks/timeline/use-edge-auto-scroll";

 import type { ElementDragState } from "@/lib/timeline";

 import { useEditor } from "@/hooks/use-editor";

@@ -59,7 +60,7 @@ export function TimelineTrackContent({
 		getMouseClientX: () => lastMouseXRef.current ?? 0,

 		rulerScrollRef,

 		tracksScrollRef,

-		contentWidth: duration * TIMELINE_CONSTANTS.PIXELS_PER_SECOND * zoomLevel,

+		contentWidth: duration * BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel,

 	});

 

 	return (

diff --git a/apps/web/src/components/editor/panels/timeline/track-layout.ts b/apps/web/src/components/editor/panels/timeline/track-layout.ts
new file mode 100644
index 00000000..89cc4d05
--- /dev/null
+++ b/apps/web/src/components/editor/panels/timeline/track-layout.ts
@@ -0,0 +1,37 @@
+import type { TrackType } from "@/lib/timeline";
+import {
+	TIMELINE_TRACK_GAP_PX,
+	TIMELINE_TRACK_HEIGHTS_PX,
+} from "./layout";
+
+export function getTrackHeight({ type }: { type: TrackType }): number {
+	return TIMELINE_TRACK_HEIGHTS_PX[type];
+}
+
+export function getCumulativeHeightBefore({
+	tracks,
+	trackIndex,
+}: {
+	tracks: Array<{ type: TrackType }>;
+	trackIndex: number;
+}): number {
+	return tracks
+		.slice(0, trackIndex)
+		.reduce(
+			(sum, track) => sum + getTrackHeight({ type: track.type }) + TIMELINE_TRACK_GAP_PX,
+			0,
+		);
+}
+
+export function getTotalTracksHeight({
+	tracks,
+}: {
+	tracks: Array<{ type: TrackType }>;
+}): number {
+	const tracksHeight = tracks.reduce(
+		(sum, track) => sum + getTrackHeight({ type: track.type }),
+		0,
+	);
+	const gapsHeight = Math.max(0, tracks.length - 1) * TIMELINE_TRACK_GAP_PX;
+	return tracksHeight + gapsHeight;
+}