fix: model editor time as wasm MediaTime ticks end-to-end

79 files changed, 1589 insertions, 511 deletions

diff --git a/apps/web/src/actions/use-editor-actions.ts b/apps/web/src/actions/use-editor-actions.ts
index e62a8ce0..5e90a6a1 100644
--- a/apps/web/src/actions/use-editor-actions.ts
+++ b/apps/web/src/actions/use-editor-actions.ts
@@ -5,7 +5,16 @@ import { useTimelineStore } from "@/timeline/timeline-store";
 import { useActionHandler } from "@/actions/use-action-handler";
 import { useEditor } from "@/editor/use-editor";
 import { useElementSelection } from "@/timeline/hooks/element/use-element-selection";
-import { TICKS_PER_SECOND } from "@/wasm";
+import {
+	addMediaTime,
+	maxMediaTime,
+	mediaTime,
+	mediaTimeFromSeconds,
+	minMediaTime,
+	subMediaTime,
+	TICKS_PER_SECOND,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 import { useKeyframeSelection } from "@/timeline/hooks/element/use-keyframe-selection";
 import { getElementsAtTime, hasMediaId } from "@/timeline";
 import { cancelInteraction } from "@/editor/cancel-interaction";
@@ -83,7 +92,7 @@ export function useEditorActions() {
 			if (editor.playback.getIsPlaying()) {
 				editor.playback.toggle();
 			}
-			editor.playback.seek({ time: 0 });
+			editor.playback.seek({ time: ZERO_MEDIA_TIME });
 		},
 		undefined,
 	);
@@ -92,11 +101,15 @@ export function useEditorActions() {
 		"seek-forward",
 		(args) => {
 			const seconds = args?.seconds ?? 1;
+			const delta = mediaTimeFromSeconds({ seconds });
 			editor.playback.seek({
-				time: Math.min(
-					editor.timeline.getTotalDuration(),
-					editor.playback.getCurrentTime() + seconds,
-				),
+				time: minMediaTime({
+					a: editor.timeline.getTotalDuration(),
+					b: addMediaTime({
+						a: editor.playback.getCurrentTime(),
+						b: delta,
+					}),
+				}),
 			});
 		},
 		undefined,
@@ -106,8 +119,15 @@ export function useEditorActions() {
 		"seek-backward",
 		(args) => {
 			const seconds = args?.seconds ?? 1;
+			const delta = mediaTimeFromSeconds({ seconds });
 			editor.playback.seek({
-				time: Math.max(0, editor.playback.getCurrentTime() - seconds),
+				time: maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: subMediaTime({
+						a: editor.playback.getCurrentTime(),
+						b: delta,
+					}),
+				}),
 			});
 		},
 		undefined,
@@ -117,15 +137,20 @@ export function useEditorActions() {
 		"frame-step-forward",
 		() => {
 			const fps = editor.project.getActive().settings.fps;
-			const ticksPerFrame = Math.round(
-				(TICKS_PER_SECOND * fps.denominator) / fps.numerator,
-			);
-			editor.playback.seek({
-				time: Math.min(
-					editor.timeline.getTotalDuration(),
-					editor.playback.getCurrentTime() + ticksPerFrame,
+			const ticksPerFrame = mediaTime({
+				ticks: Math.round(
+					(TICKS_PER_SECOND * fps.denominator) / fps.numerator,
 				),
 			});
+			editor.playback.seek({
+				time: minMediaTime({
+					a: editor.timeline.getTotalDuration(),
+					b: addMediaTime({
+						a: editor.playback.getCurrentTime(),
+						b: ticksPerFrame,
+					}),
+				}),
+			});
 		},
 		undefined,
 	);
@@ -134,11 +159,19 @@ export function useEditorActions() {
 		"frame-step-backward",
 		() => {
 			const fps = editor.project.getActive().settings.fps;
-			const ticksPerFrame = Math.round(
-				(TICKS_PER_SECOND * fps.denominator) / fps.numerator,
-			);
+			const ticksPerFrame = mediaTime({
+				ticks: Math.round(
+					(TICKS_PER_SECOND * fps.denominator) / fps.numerator,
+				),
+			});
 			editor.playback.seek({
-				time: Math.max(0, editor.playback.getCurrentTime() - ticksPerFrame),
+				time: maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: subMediaTime({
+						a: editor.playback.getCurrentTime(),
+						b: ticksPerFrame,
+					}),
+				}),
 			});
 		},
 		undefined,
@@ -148,11 +181,15 @@ export function useEditorActions() {
 		"jump-forward",
 		(args) => {
 			const seconds = args?.seconds ?? 5;
+			const delta = mediaTimeFromSeconds({ seconds });
 			editor.playback.seek({
-				time: Math.min(
-					editor.timeline.getTotalDuration(),
-					editor.playback.getCurrentTime() + seconds,
-				),
+				time: minMediaTime({
+					a: editor.timeline.getTotalDuration(),
+					b: addMediaTime({
+						a: editor.playback.getCurrentTime(),
+						b: delta,
+					}),
+				}),
 			});
 		},
 		undefined,
@@ -162,8 +199,15 @@ export function useEditorActions() {
 		"jump-backward",
 		(args) => {
 			const seconds = args?.seconds ?? 5;
+			const delta = mediaTimeFromSeconds({ seconds });
 			editor.playback.seek({
-				time: Math.max(0, editor.playback.getCurrentTime() - seconds),
+				time: maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: subMediaTime({
+						a: editor.playback.getCurrentTime(),
+						b: delta,
+					}),
+				}),
 			});
 		},
 		undefined,
@@ -172,7 +216,7 @@ export function useEditorActions() {
 	useActionHandler(
 		"goto-start",
 		() => {
-			editor.playback.seek({ time: 0 });
+			editor.playback.seek({ time: ZERO_MEDIA_TIME });
 		},
 		undefined,
 	);
diff --git a/apps/web/src/animation/curve-bridge.ts b/apps/web/src/animation/curve-bridge.ts
index af411dd1..c947e7dc 100644
--- a/apps/web/src/animation/curve-bridge.ts
+++ b/apps/web/src/animation/curve-bridge.ts
@@ -7,6 +7,7 @@ import type {
 	NormalizedCubicBezier,
 	ScalarAnimationKey,
 } from "@/animation/types";
+import { roundMediaTime } from "@/wasm";
 
 const VALUE_EPSILON = 1e-6;
 
@@ -84,11 +85,11 @@ export function getCurveHandlesForNormalizedCubicBezier({
 
 	return {
 		rightHandle: {
-			dt: spanTime * x1,
+			dt: roundMediaTime({ time: spanTime * x1 }),
 			dv: effectiveSpanValue * y1,
 		},
 		leftHandle: {
-			dt: spanTime * (x2 - 1),
+			dt: roundMediaTime({ time: spanTime * (x2 - 1) }),
 			dv: effectiveSpanValue * (y2 - 1),
 		},
 	};
diff --git a/apps/web/src/animation/interpolation.ts b/apps/web/src/animation/interpolation.ts
index 277bfbb7..2169024a 100644
--- a/apps/web/src/animation/interpolation.ts
+++ b/apps/web/src/animation/interpolation.ts
@@ -9,6 +9,7 @@ import type {
 	ScalarSegmentType,
 } from "@/animation/types";
 import { clamp } from "@/utils/math";
+import { mediaTime } from "@/wasm";
 import {
 	getBezierPoint,
 	getDefaultLeftHandle,
@@ -63,9 +64,13 @@ function normalizeRightHandle({
 		return undefined;
 	}
 
-	const span = Math.max(1, rightKey.time - leftKey.time);
+	const span = mediaTime({
+		ticks: Math.max(1, rightKey.time - leftKey.time),
+	});
 	return {
-		dt: Math.min(span, Math.max(0, handle.dt)),
+		dt: mediaTime({
+			ticks: Math.min(span, Math.max(0, handle.dt)),
+		}),
 		dv: handle.dv,
 	};
 }
@@ -83,9 +88,13 @@ function normalizeLeftHandle({
 		return undefined;
 	}
 
-	const span = Math.max(1, rightKey.time - leftKey.time);
+	const span = mediaTime({
+		ticks: Math.max(1, rightKey.time - leftKey.time),
+	});
 	return {
-		dt: Math.max(-span, Math.min(0, handle.dt)),
+		dt: mediaTime({
+			ticks: Math.max(-span, Math.min(0, handle.dt)),
+		}),
 		dv: handle.dv,
 	};
 }
diff --git a/apps/web/src/animation/keyframes.ts b/apps/web/src/animation/keyframes.ts
index 12dc777d..bdfe7c4c 100644
--- a/apps/web/src/animation/keyframes.ts
+++ b/apps/web/src/animation/keyframes.ts
@@ -35,6 +35,12 @@ import {
 	coerceAnimationValueForProperty,
 	getAnimationPropertyDefinition,
 } from "./property-registry";
+import {
+	type MediaTime,
+	roundMediaTime,
+	subMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 function isNearlySameTime({
 	leftTime,
@@ -171,7 +177,7 @@ function createScalarKey({
 	previousKey,
 }: {
 	id: string;
-	time: number;
+	time: MediaTime;
 	value: number;
 	interpolation?: AnimationInterpolation;
 	previousKey?: ScalarAnimationKey;
@@ -195,7 +201,7 @@ function createDiscreteKey({
 	value,
 }: {
 	id: string;
-	time: number;
+	time: MediaTime;
 	value: string | boolean;
 }): DiscreteAnimationKey {
 	return {
@@ -241,7 +247,7 @@ function getTargetKeyMetadata({
 	keyframeId,
 }: {
 	channel: AnimationChannel | undefined;
-	time: number;
+	time: MediaTime;
 	keyframeId?: string;
 }) {
 	const normalizedChannel =
@@ -280,7 +286,7 @@ function upsertDiscreteChannelKey({
 	keyframeId,
 }: {
 	channel: DiscreteAnimationChannel | undefined;
-	time: number;
+	time: MediaTime;
 	value: string | boolean;
 	keyframeId?: string;
 }): DiscreteAnimationChannel {
@@ -337,7 +343,7 @@ function upsertScalarChannelKey({
 	keyframeId,
 }: {
 	channel: ScalarAnimationChannel | undefined;
-	time: number;
+	time: MediaTime;
 	value: number;
 	interpolation?: AnimationInterpolation;
 	defaultInterpolation?: AnimationInterpolation;
@@ -442,7 +448,7 @@ export function upsertPathKeyframe({
 }: {
 	animations: ElementAnimations | undefined;
 	propertyPath: AnimationPath;
-	time: number;
+	time: MediaTime;
 	value: AnimationValue;
 	interpolation?: AnimationInterpolation;
 	keyframeId?: string;
@@ -537,7 +543,7 @@ export function upsertElementKeyframe({
 }: {
 	animations: ElementAnimations | undefined;
 	propertyPath: AnimationPropertyPath;
-	time: number;
+	time: MediaTime;
 	value: AnimationValue;
 	interpolation?: AnimationInterpolation;
 	keyframeId?: string;
@@ -576,7 +582,7 @@ export function upsertKeyframe({
 	keyframeId,
 }: {
 	channel: AnimationChannel | undefined;
-	time: number;
+	time: MediaTime;
 	value: AnimationValue;
 	interpolation?: AnimationInterpolation;
 	keyframeId?: string;
@@ -642,7 +648,7 @@ export function retimeKeyframe({
 }: {
 	channel: AnimationChannel | undefined;
 	keyframeId: string;
-	time: number;
+	time: MediaTime;
 }): AnimationChannel | undefined {
 	if (!channel) {
 		return undefined;
@@ -887,7 +893,7 @@ export function clampAnimationsToDuration({
 	duration,
 }: {
 	animations: ElementAnimations | undefined;
-	duration: number;
+	duration: MediaTime;
 }): ElementAnimations | undefined {
 	if (!animations || duration <= 0) {
 		return undefined;
@@ -923,7 +929,7 @@ function splitDiscreteChannelAtTime({
 	shouldIncludeSplitBoundary,
 }: {
 	channel: DiscreteAnimationChannel | undefined;
-	splitTime: number;
+	splitTime: MediaTime;
 	leftBoundaryId: string;
 	rightBoundaryId: string;
 	shouldIncludeSplitBoundary: boolean;
@@ -939,7 +945,10 @@ function splitDiscreteChannelAtTime({
 	let leftKeys = normalizedChannel.keys.filter((key) => key.time <= splitTime);
 	let rightKeys = normalizedChannel.keys
 		.filter((key) => key.time >= splitTime)
-		.map((key) => ({ ...key, time: key.time - splitTime }));
+		.map((key) => ({
+			...key,
+			time: subMediaTime({ a: key.time, b: splitTime }),
+		}));
 
 	if (shouldIncludeSplitBoundary) {
 		const hasBoundaryOnLeft = leftKeys.some((key) =>
@@ -967,7 +976,7 @@ function splitDiscreteChannelAtTime({
 			rightKeys = [
 				createDiscreteKey({
 					id: rightBoundaryId,
-					time: 0,
+					time: ZERO_MEDIA_TIME,
 					value: boundaryValue as string | boolean,
 				}),
 				...rightKeys,
@@ -993,7 +1002,7 @@ function splitScalarChannelAtTime({
 	shouldIncludeSplitBoundary,
 }: {
 	channel: ScalarAnimationChannel | undefined;
-	splitTime: number;
+	splitTime: MediaTime;
 	leftBoundaryId: string;
 	rightBoundaryId: string;
 	shouldIncludeSplitBoundary: boolean;
@@ -1009,7 +1018,10 @@ function splitScalarChannelAtTime({
 	let leftKeys = normalizedChannel.keys.filter((key) => key.time <= splitTime);
 	let rightKeys = normalizedChannel.keys
 		.filter((key) => key.time >= splitTime)
-		.map((key) => ({ ...key, time: key.time - splitTime }));
+		.map((key) => ({
+			...key,
+			time: subMediaTime({ a: key.time, b: splitTime }),
+		}));
 
 	const hasBoundaryOnLeft = leftKeys.some((key) =>
 		isNearlySameTime({ leftTime: key.time, rightTime: splitTime }),
@@ -1089,7 +1101,7 @@ function splitScalarChannelAtTime({
 				{
 					...leftKey,
 					rightHandle: {
-						dt: q0.x - p0.x,
+						dt: roundMediaTime({ time: q0.x - p0.x }),
 						dv: q0.y - p0.y,
 					},
 				},
@@ -1098,7 +1110,7 @@ function splitScalarChannelAtTime({
 					time: splitTime,
 					value: boundaryValue,
 					leftHandle: {
-						dt: r0.x - splitPoint.x,
+						dt: roundMediaTime({ time: r0.x - splitPoint.x }),
 						dv: r0.y - splitPoint.y,
 					},
 					segmentToNext: leftKey.segmentToNext,
@@ -1108,10 +1120,10 @@ function splitScalarChannelAtTime({
 			rightKeys = [
 				{
 					id: rightBoundaryId,
-					time: 0,
+					time: ZERO_MEDIA_TIME,
 					value: boundaryValue,
 					rightHandle: {
-						dt: r1.x - splitPoint.x,
+						dt: roundMediaTime({ time: r1.x - splitPoint.x }),
 						dv: r1.y - splitPoint.y,
 					},
 					segmentToNext: "bezier",
@@ -1119,9 +1131,9 @@ function splitScalarChannelAtTime({
 				},
 				{
 					...rightKey,
-					time: rightKey.time - splitTime,
+					time: subMediaTime({ a: rightKey.time, b: splitTime }),
 					leftHandle: {
-						dt: q2.x - p3.x,
+						dt: roundMediaTime({ time: q2.x - p3.x }),
 						dv: q2.y - p3.y,
 					},
 				},
@@ -1129,7 +1141,7 @@ function splitScalarChannelAtTime({
 					.filter((key) => key.time > rightKey.time)
 					.map((key) => ({
 						...key,
-						time: key.time - splitTime,
+						time: subMediaTime({ a: key.time, b: splitTime }),
 					})),
 			];
 		} else {
@@ -1145,7 +1157,7 @@ function splitScalarChannelAtTime({
 			rightKeys = [
 				createScalarKey({
 					id: rightBoundaryId,
-					time: 0,
+					time: ZERO_MEDIA_TIME,
 					value: boundaryValue,
 					interpolation: getScalarSegmentInterpolation({
 						segment: leftKey.segmentToNext,
@@ -1201,7 +1213,7 @@ export function splitAnimationsAtTime({
 	shouldIncludeSplitBoundary = true,
 }: {
 	animations: ElementAnimations | undefined;
-	splitTime: number;
+	splitTime: MediaTime;
 	shouldIncludeSplitBoundary?: boolean;
 }): {
 	leftAnimations: ElementAnimations | undefined;
@@ -1317,7 +1329,7 @@ export function retimeElementKeyframe({
 	animations: ElementAnimations | undefined;
 	propertyPath: AnimationPath;
 	keyframeId: string;
-	time: number;
+	time: MediaTime;
 }): ElementAnimations | undefined {
 	const binding = getBinding({ animations, propertyPath });
 	if (!binding) {
diff --git a/apps/web/src/animation/types.ts b/apps/web/src/animation/types.ts
index 3afddfa1..e02c8ba8 100644
--- a/apps/web/src/animation/types.ts
+++ b/apps/web/src/animation/types.ts
@@ -1,4 +1,5 @@
 import type { ParamValues } from "@/params";
+import type { MediaTime } from "@/wasm";
 
 export const ANIMATION_PROPERTY_PATHS = [
 	"transform.positionX",
@@ -77,13 +78,13 @@ export type TangentMode = "auto" | "aligned" | "broken" | "flat";
 export type ChannelExtrapolationMode = "hold" | "linear";
 
 export interface CurveHandle {
-	dt: number;
+	dt: MediaTime;
 	dv: number;
 }
 
 interface BaseAnimationKeyframe<TValue extends number | DiscreteValue> {
 	id: string;
-	time: number; // relative to element start time
+	time: MediaTime; // relative to element start time
 	value: TValue;
 }
 
@@ -209,7 +210,7 @@ export interface ScalarCurveKeyframePatch {
 export interface ElementKeyframe {
 	propertyPath: AnimationPath;
 	id: string;
-	time: number;
+	time: MediaTime;
 	value: AnimationValue;
 	interpolation: AnimationInterpolation;
 }
diff --git a/apps/web/src/clipboard/handlers/keyframes.ts b/apps/web/src/clipboard/handlers/keyframes.ts
index ad156e12..cb0c0e65 100644
--- a/apps/web/src/clipboard/handlers/keyframes.ts
+++ b/apps/web/src/clipboard/handlers/keyframes.ts
@@ -7,6 +7,7 @@ import type {
 	KeyframeClipboardCurvePatch,
 	KeyframeClipboardItem,
 } from "../types";
+import { roundMediaTime, subMediaTime, type MediaTime } from "@/wasm";
 
 function resolveSingleSourceElement({
 	selectedKeyframes,
@@ -80,7 +81,7 @@ function buildClipboardItem({
 	element: TimelineElement;
 	propertyPath: KeyframeClipboardItem["propertyPath"];
 	keyframeId: string;
-}): (Omit<KeyframeClipboardItem, "timeOffset"> & { time: number }) | null {
+}): (Omit<KeyframeClipboardItem, "timeOffset"> & { time: MediaTime }) | null {
 	const keyframe = getKeyframeById({
 		animations: element.animations,
 		propertyPath,
@@ -136,10 +137,11 @@ export const KeyframesClipboardHandler = {
 		}
 
 		const minTime = Math.min(...rawItems.map((item) => item.time));
+		const minTimeMedia = roundMediaTime({ time: minTime });
 		const items = rawItems
 			.map(({ time, ...item }) => ({
 				...item,
-				timeOffset: time - minTime,
+				timeOffset: subMediaTime({ a: time, b: minTimeMedia }),
 			}))
 			.sort(
 				(left, right) =>
diff --git a/apps/web/src/clipboard/types.ts b/apps/web/src/clipboard/types.ts
index 0d249c9d..562f9ac7 100644
--- a/apps/web/src/clipboard/types.ts
+++ b/apps/web/src/clipboard/types.ts
@@ -12,6 +12,7 @@ import type {
 	ElementRef,
 	TrackType,
 } from "@/timeline";
+import type { MediaTime } from "@/wasm";
 
 export interface ElementClipboardItem {
 	trackId: string;
@@ -26,7 +27,7 @@ export interface KeyframeClipboardCurvePatch {
 
 export interface KeyframeClipboardItem {
 	propertyPath: AnimationPath;
-	timeOffset: number;
+	timeOffset: MediaTime;
 	value: AnimationValue;
 	interpolation: AnimationInterpolation;
 	curvePatches: KeyframeClipboardCurvePatch[];
@@ -61,7 +62,7 @@ export interface PasteContext {
 	editor: EditorCore;
 	selectedElements: ElementRef[];
 	selectedKeyframes: SelectedKeyframeRef[];
-	time: number;
+	time: MediaTime;
 }
 
 export interface ClipboardHandler<TType extends ClipboardEntryType> {
diff --git a/apps/web/src/commands/scene/move-bookmark.ts b/apps/web/src/commands/scene/move-bookmark.ts
index a1624eb0..f3628b28 100644
--- a/apps/web/src/commands/scene/move-bookmark.ts
+++ b/apps/web/src/commands/scene/move-bookmark.ts
@@ -3,13 +3,14 @@ import { EditorCore } from "@/core";
 import type { TScene } from "@/timeline";
 import { updateSceneInArray } from "@/timeline/scenes";
 import { getFrameTime, moveBookmarkInArray } from "@/timeline/bookmarks/index";
+import type { MediaTime } from "@/wasm";
 
 export class MoveBookmarkCommand extends Command {
 	private savedScenes: TScene[] | null = null;
 
 	constructor(
-		private fromTime: number,
-		private toTime: number,
+		private fromTime: MediaTime,
+		private toTime: MediaTime,
 	) {
 		super();
 	}
diff --git a/apps/web/src/commands/scene/remove-bookmark.ts b/apps/web/src/commands/scene/remove-bookmark.ts
index ea592556..bff5c035 100644
--- a/apps/web/src/commands/scene/remove-bookmark.ts
+++ b/apps/web/src/commands/scene/remove-bookmark.ts
@@ -6,12 +6,13 @@ import {
 	getFrameTime,
 	removeBookmarkFromArray,
 } from "@/timeline/bookmarks/index";
+import type { MediaTime } from "@/wasm";
 
 export class RemoveBookmarkCommand extends Command {
 	private savedScenes: TScene[] | null = null;
-	private frameTime: number = 0;
+	private frameTime: MediaTime = 0 as MediaTime;
 
-	constructor(private time: number) {
+	constructor(private time: MediaTime) {
 		super();
 	}
 
diff --git a/apps/web/src/commands/scene/toggle-bookmark.ts b/apps/web/src/commands/scene/toggle-bookmark.ts
index 4193c76e..9f318f80 100644
--- a/apps/web/src/commands/scene/toggle-bookmark.ts
+++ b/apps/web/src/commands/scene/toggle-bookmark.ts
@@ -6,12 +6,13 @@ import {
 	getFrameTime,
 	toggleBookmarkInArray,
 } from "@/timeline/bookmarks/index";
+import type { MediaTime } from "@/wasm";
 
 export class ToggleBookmarkCommand extends Command {
 	private savedScenes: TScene[] | null = null;
-	private frameTime: number = 0;
+	private frameTime: MediaTime = 0 as MediaTime;
 
-	constructor(private time: number) {
+	constructor(private time: MediaTime) {
 		super();
 	}
 
diff --git a/apps/web/src/commands/scene/update-bookmark.ts b/apps/web/src/commands/scene/update-bookmark.ts
index 0d6a0193..238bb3de 100644
--- a/apps/web/src/commands/scene/update-bookmark.ts
+++ b/apps/web/src/commands/scene/update-bookmark.ts
@@ -6,12 +6,13 @@ import {
 	getFrameTime,
 	updateBookmarkInArray,
 } from "@/timeline/bookmarks/index";
+import type { MediaTime } from "@/wasm";
 
 export class UpdateBookmarkCommand extends Command {
 	private savedScenes: TScene[] | null = null;
 
 	constructor(
-		private time: number,
+		private time: MediaTime,
 		private updates: Partial<Omit<Bookmark, "time">>,
 	) {
 		super();
diff --git a/apps/web/src/commands/timeline/clipboard/paste-keyframes.ts b/apps/web/src/commands/timeline/clipboard/paste-keyframes.ts
index e05b49fa..c1127921 100644
--- a/apps/web/src/commands/timeline/clipboard/paste-keyframes.ts
+++ b/apps/web/src/commands/timeline/clipboard/paste-keyframes.ts
@@ -10,6 +10,13 @@ import type { KeyframeClipboardItem } from "@/clipboard";
 import type { SceneTracks, TimelineElement } from "@/timeline";
 import { updateElementInSceneTracks } from "@/timeline";
 import { generateUUID } from "@/utils/id";
+import {
+	addMediaTime,
+	type MediaTime,
+	maxMediaTime,
+	minMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 function pasteKeyframesIntoElement({
 	element,
@@ -17,7 +24,7 @@ function pasteKeyframesIntoElement({
 	clipboardItems,
 }: {
 	element: TimelineElement;
-	time: number;
+	time: MediaTime;
 	clipboardItems: KeyframeClipboardItem[];
 }): TimelineElement {
 	let nextElement = element;
@@ -31,10 +38,13 @@ function pasteKeyframesIntoElement({
 			continue;
 		}
 
-		const keyframeTime = Math.max(
-			0,
-			Math.min(time + item.timeOffset, nextElement.duration),
-		);
+		const keyframeTime = maxMediaTime({
+			a: ZERO_MEDIA_TIME,
+			b: minMediaTime({
+				a: addMediaTime({ a: time, b: item.timeOffset }),
+				b: nextElement.duration,
+			}),
+		});
 		const nextAnimations = upsertPathKeyframe({
 			animations: nextElement.animations,
 			propertyPath: item.propertyPath,
@@ -79,7 +89,7 @@ export class PasteKeyframesCommand extends Command {
 	private savedState: SceneTracks | null = null;
 	private readonly trackId: string;
 	private readonly elementId: string;
-	private readonly time: number;
+	private readonly time: MediaTime;
 	private readonly clipboardItems: KeyframeClipboardItem[];
 
 	constructor({
@@ -90,7 +100,7 @@ export class PasteKeyframesCommand extends Command {
 	}: {
 		trackId: string;
 		elementId: string;
-		time: number;
+		time: MediaTime;
 		clipboardItems: KeyframeClipboardItem[];
 	}) {
 		super();
diff --git a/apps/web/src/commands/timeline/clipboard/paste.ts b/apps/web/src/commands/timeline/clipboard/paste.ts
index 4523566e..be0c2b91 100644
--- a/apps/web/src/commands/timeline/clipboard/paste.ts
+++ b/apps/web/src/commands/timeline/clipboard/paste.ts
@@ -13,18 +13,25 @@ import {
 	enforceMainTrackStart,
 } from "@/timeline/placement";
 import { cloneAnimations } from "@/animation";
+import {
+	addMediaTime,
+	type MediaTime,
+	maxMediaTime,
+	subMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 export class PasteCommand extends Command {
 	private savedState: SceneTracks | null = null;
 	private pastedElements: { trackId: string; elementId: string }[] = [];
-	private readonly time: number;
+	private readonly time: MediaTime;
 	private readonly clipboardItems: ElementClipboardItem[];
 
 	constructor({
 		time,
 		clipboardItems,
 	}: {
-		time: number;
+		time: MediaTime;
 		clipboardItems: ElementClipboardItem[];
 	}) {
 		super();
@@ -39,8 +46,12 @@ export class PasteCommand extends Command {
 		this.savedState = editor.scenes.getActiveScene().tracks;
 		this.pastedElements = [];
 
-		const minStart = Math.min(
-			...this.clipboardItems.map((item) => item.element.startTime),
+		const minStart = this.clipboardItems.reduce(
+			(earliestStartTime, item) =>
+				item.element.startTime < earliestStartTime
+					? item.element.startTime
+					: earliestStartTime,
+			this.clipboardItems[0].element.startTime,
 		);
 
 		let updatedTracks = this.savedState;
@@ -97,12 +108,18 @@ export class PasteCommand extends Command {
 						targetTrackId: targetTrack.id,
 						requestedStartTime: earliestElement.startTime,
 					});
-					const delta = adjustedEarliestStartTime - earliestElement.startTime;
+					const delta = subMediaTime({
+						a: adjustedEarliestStartTime,
+						b: earliestElement.startTime,
+					});
 
-					if (delta !== 0) {
+					if (delta !== ZERO_MEDIA_TIME) {
 						elementsForPlacement = elementsToAdd.map((element) => ({
 							...element,
-							startTime: Math.max(0, element.startTime + delta),
+							startTime: maxMediaTime({
+								a: ZERO_MEDIA_TIME,
+								b: addMediaTime({ a: element.startTime, b: delta }),
+							}),
 						}));
 					}
 				}
@@ -168,14 +185,20 @@ function buildPastedElements({
 	time,
 }: {
 	items: ElementClipboardItem[];
-	minStart: number;
-	time: number;
+	minStart: MediaTime;
+	time: MediaTime;
 }): TimelineElement[] {
 	const elementsToAdd: TimelineElement[] = [];
 
 	for (const item of items) {
-		const relativeOffset = item.element.startTime - minStart;
-		const startTime = Math.max(0, time + relativeOffset);
+		const relativeOffset = subMediaTime({
+			a: item.element.startTime,
+			b: minStart,
+		});
+		const startTime = maxMediaTime({
+			a: ZERO_MEDIA_TIME,
+			b: addMediaTime({ a: time, b: relativeOffset }),
+		});
 		const newElementId = generateUUID();
 
 		elementsToAdd.push({
diff --git a/apps/web/src/commands/timeline/element/duplicate-elements.ts b/apps/web/src/commands/timeline/element/duplicate-elements.ts
index 8f65f7c7..2b1ab4ea 100644
--- a/apps/web/src/commands/timeline/element/duplicate-elements.ts
+++ b/apps/web/src/commands/timeline/element/duplicate-elements.ts
@@ -8,6 +8,7 @@ import { generateUUID } from "@/utils/id";
 import { EditorCore } from "@/core";
 import { applyPlacement, resolveTrackPlacement } from "@/timeline/placement";
 import { cloneAnimations } from "@/animation";
+import type { MediaTime } from "@/wasm";
 
 interface DuplicateElementsParams {
 	elements: { trackId: string; elementId: string }[];
@@ -119,7 +120,7 @@ function buildDuplicateElement({
 }: {
 	element: TimelineElement;
 	id: string;
-	startTime: number;
+	startTime: MediaTime;
 }): TimelineElement {
 	return {
 		...element,
diff --git a/apps/web/src/commands/timeline/element/insert-element.ts b/apps/web/src/commands/timeline/element/insert-element.ts
index 49ac6f2d..2110d67b 100644
--- a/apps/web/src/commands/timeline/element/insert-element.ts
+++ b/apps/web/src/commands/timeline/element/insert-element.ts
@@ -18,6 +18,7 @@ import {
 	resolveTrackPlacement,
 	validateElementTrackCompatibility,
 } from "@/timeline/placement";
+import { roundMediaTime } from "@/wasm";
 
 type InsertElementPlacement =
 	| { mode: "explicit"; trackId: string }
@@ -266,7 +267,12 @@ export class InsertElementCommand extends Command {
 			placementResult.kind === "existingTrack"
 				? {
 						...element,
-						startTime: placementResult.adjustedStartTime ?? element.startTime,
+						startTime:
+							placementResult.adjustedStartTime !== undefined
+								? roundMediaTime({
+										time: placementResult.adjustedStartTime,
+									})
+								: element.startTime,
 					}
 				: element;
 
diff --git a/apps/web/src/commands/timeline/element/keyframes/retime-keyframe.ts b/apps/web/src/commands/timeline/element/keyframes/retime-keyframe.ts
index ccbdbc5d..9337e02d 100644
--- a/apps/web/src/commands/timeline/element/keyframes/retime-keyframe.ts
+++ b/apps/web/src/commands/timeline/element/keyframes/retime-keyframe.ts
@@ -4,6 +4,12 @@ import { Command, type CommandResult } from "@/commands/base-command";
 import { updateElementInSceneTracks } from "@/timeline";
 import type { AnimationPath } from "@/animation/types";
 import type { SceneTracks } from "@/timeline";
+import {
+	type MediaTime,
+	maxMediaTime,
+	minMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 export class RetimeKeyframeCommand extends Command {
 	private savedState: SceneTracks | null = null;
@@ -11,7 +17,7 @@ export class RetimeKeyframeCommand extends Command {
 	private readonly elementId: string;
 	private readonly propertyPath: AnimationPath;
 	private readonly keyframeId: string;
-	private readonly nextTime: number;
+	private readonly nextTime: MediaTime;
 
 	constructor({
 		trackId,
@@ -24,7 +30,7 @@ export class RetimeKeyframeCommand extends Command {
 		elementId: string;
 		propertyPath: AnimationPath;
 		keyframeId: string;
-		nextTime: number;
+		nextTime: MediaTime;
 	}) {
 		super();
 		this.trackId = trackId;
@@ -47,7 +53,10 @@ export class RetimeKeyframeCommand extends Command {
 					return element;
 				}
 
-				const boundedTime = Math.max(0, Math.min(this.nextTime, element.duration));
+				const boundedTime = maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: minMediaTime({ a: this.nextTime, b: element.duration }),
+				});
 				return {
 					...element,
 					animations: retimeElementKeyframe({
diff --git a/apps/web/src/commands/timeline/element/keyframes/upsert-effect-param-keyframe.ts b/apps/web/src/commands/timeline/element/keyframes/upsert-effect-param-keyframe.ts
index eae8f039..91ddb23d 100644
--- a/apps/web/src/commands/timeline/element/keyframes/upsert-effect-param-keyframe.ts
+++ b/apps/web/src/commands/timeline/element/keyframes/upsert-effect-param-keyframe.ts
@@ -9,6 +9,12 @@ import { updateElementInSceneTracks } from "@/timeline";
 import { isVisualElement } from "@/timeline/element-utils";
 import type { AnimationInterpolation } from "@/animation/types";
 import type { SceneTracks } from "@/timeline";
+import {
+	type MediaTime,
+	maxMediaTime,
+	minMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 export class UpsertEffectParamKeyframeCommand extends Command {
 	private savedState: SceneTracks | null = null;
@@ -16,7 +22,7 @@ export class UpsertEffectParamKeyframeCommand extends Command {
 	private readonly elementId: string;
 	private readonly effectId: string;
 	private readonly paramKey: string;
-	private readonly time: number;
+	private readonly time: MediaTime;
 	private readonly value: number | string | boolean;
 	private readonly interpolation: AnimationInterpolation | undefined;
 	private readonly keyframeId: string | undefined;
@@ -35,7 +41,7 @@ export class UpsertEffectParamKeyframeCommand extends Command {
 		elementId: string;
 		effectId: string;
 		paramKey: string;
-		time: number;
+		time: MediaTime;
 		value: number | string | boolean;
 		interpolation?: AnimationInterpolation;
 		keyframeId?: string;
@@ -61,7 +67,10 @@ export class UpsertEffectParamKeyframeCommand extends Command {
 			elementId: this.elementId,
 			elementPredicate: isVisualElement,
 			update: (element) => {
-				const boundedTime = Math.max(0, Math.min(this.time, element.duration));
+				const boundedTime = maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: minMediaTime({ a: this.time, b: element.duration }),
+				});
 				const propertyPath = buildEffectParamPath({
 					effectId: this.effectId,
 					paramKey: this.paramKey,
diff --git a/apps/web/src/commands/timeline/element/keyframes/upsert-keyframe.ts b/apps/web/src/commands/timeline/element/keyframes/upsert-keyframe.ts
index 30514146..66f0c434 100644
--- a/apps/web/src/commands/timeline/element/keyframes/upsert-keyframe.ts
+++ b/apps/web/src/commands/timeline/element/keyframes/upsert-keyframe.ts
@@ -8,13 +8,19 @@ import type {
 	AnimationInterpolation,
 	AnimationValue,
 } from "@/animation/types";
+import {
+	type MediaTime,
+	maxMediaTime,
+	minMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 export class UpsertKeyframeCommand extends Command {
 	private savedState: SceneTracks | null = null;
 	private readonly trackId: string;
 	private readonly elementId: string;
 	private readonly propertyPath: AnimationPath;
-	private readonly time: number;
+	private readonly time: MediaTime;
 	private readonly value: AnimationValue;
 	private readonly interpolation: AnimationInterpolation | undefined;
 	private readonly keyframeId: string | undefined;
@@ -31,7 +37,7 @@ export class UpsertKeyframeCommand extends Command {
 		trackId: string;
 		elementId: string;
 		propertyPath: AnimationPath;
-		time: number;
+		time: MediaTime;
 		value: AnimationValue;
 		interpolation?: AnimationInterpolation;
 		keyframeId?: string;
@@ -63,7 +69,10 @@ export class UpsertKeyframeCommand extends Command {
 					return element;
 				}
 
-				const boundedTime = Math.max(0, Math.min(this.time, element.duration));
+				const boundedTime = maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: minMediaTime({ a: this.time, b: element.duration }),
+				});
 				return {
 					...element,
 					animations: upsertPathKeyframe({
diff --git a/apps/web/src/commands/timeline/element/split-elements.ts b/apps/web/src/commands/timeline/element/split-elements.ts
index 11c317f4..0a551fc3 100644
--- a/apps/web/src/commands/timeline/element/split-elements.ts
+++ b/apps/web/src/commands/timeline/element/split-elements.ts
@@ -9,12 +9,18 @@ import { EditorCore } from "@/core";
 import { isRetimableElement } from "@/timeline";
 import { splitAnimationsAtTime } from "@/animation";
 import { getSourceSpanAtClipTime } from "@/retime";
+import {
+	addMediaTime,
+	type MediaTime,
+	roundMediaTime,
+	subMediaTime,
+} from "@/wasm";
 
 export class SplitElementsCommand extends Command {
 	private savedState: SceneTracks | null = null;
 	private rightSideElements: { trackId: string; elementId: string }[] = [];
 	private readonly elements: { trackId: string; elementId: string }[];
-	private readonly splitTime: number;
+	private readonly splitTime: MediaTime;
 	private readonly retainSide: "both" | "left" | "right";
 
 	constructor({
@@ -23,7 +29,7 @@ export class SplitElementsCommand extends Command {
 		retainSide = "both",
 	}: {
 		elements: { trackId: string; elementId: string }[];
-		splitTime: number;
+		splitTime: MediaTime;
 		retainSide?: "both" | "left" | "right";
 	}) {
 		super();
@@ -73,21 +79,39 @@ export class SplitElementsCommand extends Command {
 					return [element];
 				}
 
-				const relativeTime = this.splitTime - element.startTime;
+				const relativeTime = subMediaTime({
+					a: this.splitTime,
+					b: element.startTime,
+				});
 				const leftVisibleDuration = relativeTime;
-				const rightVisibleDuration = element.duration - relativeTime;
+				const rightVisibleDuration = subMediaTime({
+					a: element.duration,
+					b: relativeTime,
+				});
 				const retimeRef = isRetimableElement(element)
 					? element.retime
 					: undefined;
-				const leftSourceSpan = getSourceSpanAtClipTime({
-					clipTime: leftVisibleDuration,
-					retime: retimeRef,
+				// Snap the source-side split point exactly once and derive the right
+				// half from it. Independently rounding both spans (left and total)
+				// would let a 1-tick rounding error desynchronise them, breaking the
+				// invariant `leftSourceSpan + rightSourceSpan == totalSourceSpan`.
+				// See the same discipline in `compute-resize.ts` (snap-once comment).
+				const leftSourceSpan = roundMediaTime({
+					time: getSourceSpanAtClipTime({
+						clipTime: leftVisibleDuration,
+						retime: retimeRef,
+					}),
+				});
+				const totalSourceSpan = roundMediaTime({
+					time: getSourceSpanAtClipTime({
+						clipTime: element.duration,
+						retime: retimeRef,
+					}),
 				});
-				const totalSourceSpan = getSourceSpanAtClipTime({
-					clipTime: element.duration,
-					retime: retimeRef,
+				const rightSourceSpan = subMediaTime({
+					a: totalSourceSpan,
+					b: leftSourceSpan,
 				});
-				const rightSourceSpan = totalSourceSpan - leftSourceSpan;
 				const { leftAnimations, rightAnimations } = splitAnimationsAtTime({
 					animations: element.animations,
 					splitTime: relativeTime,
@@ -95,12 +119,21 @@ export class SplitElementsCommand extends Command {
 				});
 				let splitResult: TimelineElement[];
 
+				const leftTrimEnd = addMediaTime({
+					a: element.trimEnd,
+					b: rightSourceSpan,
+				});
+				const rightTrimStart = addMediaTime({
+					a: element.trimStart,
+					b: leftSourceSpan,
+				});
+
 				if (this.retainSide === "left") {
 					splitResult = [
 						{
 							...element,
 							duration: leftVisibleDuration,
-							trimEnd: element.trimEnd + rightSourceSpan,
+							trimEnd: leftTrimEnd,
 							name: `${element.name} (left)`,
 							animations: leftAnimations,
 							...(retimeRef !== undefined ? { retime: retimeRef } : {}),
@@ -118,14 +151,13 @@ export class SplitElementsCommand extends Command {
 							id: newId,
 							startTime: this.splitTime,
 							duration: rightVisibleDuration,
-							trimStart: element.trimStart + leftSourceSpan,
+							trimStart: rightTrimStart,
 							name: `${element.name} (right)`,
 							animations: rightAnimations,
 							...(retimeRef !== undefined ? { retime: retimeRef } : {}),
 						},
 					];
 				} else {
-					// "both" - split into two pieces
 					const secondElementId = generateUUID();
 					this.rightSideElements.push({
 						trackId: track.id,
@@ -135,7 +167,7 @@ export class SplitElementsCommand extends Command {
 						{
 							...element,
 							duration: leftVisibleDuration,
-							trimEnd: element.trimEnd + rightSourceSpan,
+							trimEnd: leftTrimEnd,
 							name: `${element.name} (left)`,
 							animations: leftAnimations,
 							...(retimeRef !== undefined ? { retime: retimeRef } : {}),
@@ -145,7 +177,7 @@ export class SplitElementsCommand extends Command {
 							id: secondElementId,
 							startTime: this.splitTime,
 							duration: rightVisibleDuration,
-							trimStart: element.trimStart + leftSourceSpan,
+							trimStart: rightTrimStart,
 							name: `${element.name} (right)`,
 							animations: rightAnimations,
 							...(retimeRef !== undefined ? { retime: retimeRef } : {}),
diff --git a/apps/web/src/components/editable-timecode.tsx b/apps/web/src/components/editable-timecode.tsx
index 276cb490..8450cec2 100644
--- a/apps/web/src/components/editable-timecode.tsx
+++ b/apps/web/src/components/editable-timecode.tsx
@@ -3,13 +3,14 @@
 import { useEffect, useRef, useState } from "react";
 import { formatTimecode, parseTimecode, snappedSeekTime, type FrameRate, type TimeCodeFormat } from "opencut-wasm";
 import { cn } from "@/utils/ui";
+import type { MediaTime } from "@/wasm";
 
 interface EditableTimecodeProps {
-	time: number;
-	duration: number;
+	time: MediaTime;
+	duration: MediaTime;
 	format?: TimeCodeFormat;
 	fps: FrameRate;
-	onTimeChange?: ({ time }: { time: number }) => void;
+	onTimeChange?: ({ time }: { time: MediaTime }) => void;
 	className?: string;
 	disabled?: boolean;
 }
@@ -53,9 +54,12 @@ export function EditableTimecode({
 			return;
 		}
 
-		const clampedTime = duration
-			? (snappedSeekTime({ time: parsedTime, duration, rate: fps }) ?? parsedTime)
-			: parsedTime;
+		const clampedTime = (
+			duration
+				? (snappedSeekTime({ time: parsedTime, duration, rate: fps }) ??
+					parsedTime)
+				: parsedTime
+		) as MediaTime;
 
 		onTimeChange?.({ time: clampedTime });
 		setIsEditing(false);
diff --git a/apps/web/src/components/editor/panels/assets/draggable-item.tsx b/apps/web/src/components/editor/panels/assets/draggable-item.tsx
index 2f8bc64a..fdbf5e76 100644
--- a/apps/web/src/components/editor/panels/assets/draggable-item.tsx
+++ b/apps/web/src/components/editor/panels/assets/draggable-item.tsx
@@ -14,13 +14,14 @@ import { useEditor } from "@/editor/use-editor";
 import { clearDragData, setDragData } from "@/timeline/drag-data";

 import type { TimelineDragData } from "@/timeline/drag";

 import { cn } from "@/utils/ui";

+import type { MediaTime } from "@/wasm";

 

 export interface DraggableItemProps {

 	name: string;

 	preview: ReactNode;

 	dragData: TimelineDragData;

 	onDragStart?: ({ e }: { e: React.DragEvent }) => void;

-	onAddToTimeline?: ({ currentTime }: { currentTime: number }) => void;

+	onAddToTimeline?: ({ currentTime }: { currentTime: MediaTime }) => void;

 	aspectRatio?: number;

 	className?: string;

 	containerClassName?: string;

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 4afd22b7..c071fdc7 100644
--- a/apps/web/src/components/editor/panels/assets/views/assets.tsx
+++ b/apps/web/src/components/editor/panels/assets/views/assets.tsx
@@ -26,7 +26,7 @@ import {
 	TooltipTrigger,
 } from "@/components/ui/tooltip";
 import { DEFAULT_NEW_ELEMENT_DURATION } from "@/timeline/creation";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTimeFromSeconds, type MediaTime } from "@/wasm";
 import { useEditor } from "@/editor/use-editor";
 import { useFileUpload } from "@/media/use-file-upload";
 import { invokeAction } from "@/actions";
@@ -255,11 +255,11 @@ function MediaAssetDraggable({
 		startTime,
 	}: {
 		asset: MediaAsset;
-		startTime: number;
+		startTime: MediaTime;
 	}) => {
 		const duration =
 			asset.duration != null
-				? Math.round(asset.duration * TICKS_PER_SECOND)
+				? mediaTimeFromSeconds({ seconds: asset.duration })
 				: DEFAULT_NEW_ELEMENT_DURATION;
 		const element = buildElementFromMedia({
 			mediaId: asset.id,
diff --git a/apps/web/src/components/editor/panels/properties/hooks/use-element-playhead.ts b/apps/web/src/components/editor/panels/properties/hooks/use-element-playhead.ts
index 967156b3..83e31aec 100644
--- a/apps/web/src/components/editor/panels/properties/hooks/use-element-playhead.ts
+++ b/apps/web/src/components/editor/panels/properties/hooks/use-element-playhead.ts
@@ -1,22 +1,25 @@
 import { useEditor } from "@/editor/use-editor";
 import { getElementLocalTime } from "@/animation";
+import { addMediaTime, mediaTime, type MediaTime } from "@/wasm";
 
 export function useElementPlayhead({
 	startTime,
 	duration,
 }: {
-	startTime: number;
-	duration: number;
+	startTime: MediaTime;
+	duration: MediaTime;
 }) {
 	const playheadTime = useEditor((editor) => editor.playback.getCurrentTime());
-	const localTime = getElementLocalTime({
-		timelineTime: playheadTime,
-		elementStartTime: startTime,
-		elementDuration: duration,
+	const localTime = mediaTime({
+		ticks: getElementLocalTime({
+			timelineTime: playheadTime,
+			elementStartTime: startTime,
+			elementDuration: duration,
+		}),
 	});
 	const isPlayheadWithinElementRange =
 		playheadTime >= startTime &&
-		playheadTime <= startTime + duration;
+		playheadTime <= addMediaTime({ a: startTime, b: duration });
 
 	return { localTime, isPlayheadWithinElementRange };
 }
diff --git a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-color-property.ts b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-color-property.ts
index 734b514f..f6216208 100644
--- a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-color-property.ts
+++ b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-color-property.ts
@@ -6,6 +6,7 @@ import {
 } from "@/animation";

 import type { AnimationPropertyPath, ElementAnimations } from "@/animation/types";

 import type { TimelineElement } from "@/timeline";

+import type { MediaTime } from "@/wasm";

 

 export function useKeyframedColorProperty({

 	trackId,

@@ -21,7 +22,7 @@ export function useKeyframedColorProperty({
 	elementId: string;

 	animations: ElementAnimations | undefined;

 	propertyPath: AnimationPropertyPath;

-	localTime: number;

+	localTime: MediaTime;

 	isPlayheadWithinElementRange: boolean;

 	resolvedColor: string;

 	buildBaseUpdates: ({ value }: { value: string }) => Partial<TimelineElement>;

diff --git a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts
index 9dd39768..d52f7d97 100644
--- a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts
+++ b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-number-property.ts
@@ -8,6 +8,7 @@ import type { AnimationPropertyPath, ElementAnimations } from "@/animation/types
 import type { TimelineElement } from "@/timeline";

 import { snapToStep } from "@/utils/math";

 import { usePropertyDraft } from "./use-property-draft";

+import type { MediaTime } from "@/wasm";

 

 export function useKeyframedNumberProperty({

 	trackId,

@@ -27,7 +28,7 @@ export function useKeyframedNumberProperty({
 	elementId: string;

 	animations: ElementAnimations | undefined;

 	propertyPath: AnimationPropertyPath;

-	localTime: number;

+	localTime: MediaTime;

 	isPlayheadWithinElementRange: boolean;

 	displayValue: string;

 	parse: (input: string) => number | null;

diff --git a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-param-property.ts b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-param-property.ts
index b0b6f01a..e679f5c3 100644
--- a/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-param-property.ts
+++ b/apps/web/src/components/editor/panels/properties/hooks/use-keyframed-param-property.ts
@@ -15,6 +15,7 @@ import type {
 } from "@/animation/types";
 import type { ParamDefinition } from "@/params";
 import type { TimelineElement } from "@/timeline";
+import type { MediaTime } from "@/wasm";
 
 export interface KeyframedParamPropertyResult {
 	hasAnimatedKeyframes: boolean;
@@ -39,7 +40,7 @@ export function useKeyframedParamProperty({
 	trackId: string;
 	elementId: string;
 	animations: ElementAnimations | undefined;
-	localTime: number;
+	localTime: MediaTime;
 	isPlayheadWithinElementRange: boolean;
 	resolvedValue: number | string | boolean;
 	buildBaseUpdates: ({
diff --git a/apps/web/src/core/managers/clipboard-manager.ts b/apps/web/src/core/managers/clipboard-manager.ts
index 8a2a51c9..283a78ae 100644
--- a/apps/web/src/core/managers/clipboard-manager.ts
+++ b/apps/web/src/core/managers/clipboard-manager.ts
@@ -6,6 +6,7 @@ import {
 	type CopyContext,
 	type PasteContext,
 } from "@/clipboard";
+import type { MediaTime } from "@/wasm";
 
 export class ClipboardManager {
 	private entry: ClipboardEntry | null = null;
@@ -34,7 +35,7 @@ export class ClipboardManager {
 		return true;
 	}
 
-	paste({ time }: { time?: number } = {}): boolean {
+	paste({ time }: { time?: MediaTime } = {}): boolean {
 		if (!this.entry) {
 			return false;
 		}
@@ -64,7 +65,7 @@ export class ClipboardManager {
 		};
 	}
 
-	private getPasteContext({ time }: { time?: number }): PasteContext {
+	private getPasteContext({ time }: { time?: MediaTime }): PasteContext {
 		return {
 			editor: this.editor,
 			selectedElements: this.editor.selection.getSelectedElements(),
diff --git a/apps/web/src/core/managers/playback-manager.ts b/apps/web/src/core/managers/playback-manager.ts
index 1ea09826..6748fd42 100644
--- a/apps/web/src/core/managers/playback-manager.ts
+++ b/apps/web/src/core/managers/playback-manager.ts
@@ -1,10 +1,16 @@
 import type { EditorCore } from "@/core";
-import { TICKS_PER_SECOND } from "@/wasm";
+import {
+	addMediaTime,
+	clampMediaTime,
+	type MediaTime,
+	mediaTimeFromSeconds,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 import { roundToFrame } from "opencut-wasm";
 
 export class PlaybackManager {
 	private isPlaying = false;
-	private currentTime = 0;
+	private currentTime: MediaTime = ZERO_MEDIA_TIME;
 	private volume = 1;
 	private muted = false;
 	private previousVolume = 1;
@@ -12,7 +18,7 @@ export class PlaybackManager {
 	private listeners = new Set<() => void>();
 	private playbackTimer: number | null = null;
 	private playbackStartWallTime = 0;
-	private playbackStartTime = 0;
+	private playbackStartTime: MediaTime = ZERO_MEDIA_TIME;
 	private timelineScopeBound = false;
 
 	constructor(private editor: EditorCore) {}
@@ -38,7 +44,7 @@ export class PlaybackManager {
 		}
 
 		if (this.currentTime >= maxTime) {
-			this.seek({ time: 0 });
+			this.seek({ time: ZERO_MEDIA_TIME });
 		}
 
 		this.isPlaying = true;
@@ -60,7 +66,7 @@ export class PlaybackManager {
 		}
 	}
 
-	seek({ time }: { time: number }): void {
+	seek({ time }: { time: MediaTime }): void {
 		this.currentTime = this.clampTimeToTimeline(time);
 		if (this.isPlaying) {
 			this.playbackStartWallTime = performance.now();
@@ -107,7 +113,7 @@ export class PlaybackManager {
 		return this.isPlaying;
 	}
 
-	getCurrentTime(): number {
+	getCurrentTime(): MediaTime {
 		return this.currentTime;
 	}
 
@@ -185,11 +191,13 @@ export class PlaybackManager {
 		const fps = this.editor.project.getActive()?.settings.fps;
 		const elapsedSeconds =
 			(performance.now() - this.playbackStartWallTime) / 1000;
-		const rawTime =
-			this.playbackStartTime + Math.round(elapsedSeconds * TICKS_PER_SECOND);
-		const newTime = fps
+		const rawTime = addMediaTime({
+			a: this.playbackStartTime,
+			b: mediaTimeFromSeconds({ seconds: elapsedSeconds }),
+		});
+		const newTime = (fps
 			? (roundToFrame({ time: rawTime, rate: fps }) ?? rawTime)
-			: rawTime;
+			: rawTime) as MediaTime;
 		const maxTime = this.editor.timeline.getTotalDuration();
 
 		if (newTime >= maxTime) {
@@ -205,12 +213,12 @@ export class PlaybackManager {
 		this.playbackTimer = requestAnimationFrame(this.updateTime);
 	};
 
-	private clampTimeToTimeline(time: number): number {
+	private clampTimeToTimeline(time: MediaTime): MediaTime {
 		const maxTime = this.editor.timeline.getTotalDuration();
-		return Math.max(0, Math.min(maxTime, time));
+		return clampMediaTime({ time, min: ZERO_MEDIA_TIME, max: maxTime });
 	}
 
-	private dispatchSeekEvent(time: number): void {
+	private dispatchSeekEvent(time: MediaTime): void {
 		if (typeof window === "undefined") {
 			return;
 		}
@@ -222,7 +230,7 @@ export class PlaybackManager {
 		);
 	}
 
-	private dispatchUpdateEvent(time: number): void {
+	private dispatchUpdateEvent(time: MediaTime): void {
 		if (typeof window === "undefined") {
 			return;
 		}
diff --git a/apps/web/src/core/managers/scenes-manager.ts b/apps/web/src/core/managers/scenes-manager.ts
index 13f251a1..c9558a6d 100644
--- a/apps/web/src/core/managers/scenes-manager.ts
+++ b/apps/web/src/core/managers/scenes-manager.ts
@@ -1,5 +1,5 @@
 import type { EditorCore } from "@/core";
-import type { SceneTracks, TScene } from "@/timeline";
+import type { Bookmark, SceneTracks, TScene } from "@/timeline";
 import { storageService } from "@/services/storage/service";
 import {
 	getMainScene,
@@ -21,6 +21,7 @@ import {
 	ToggleBookmarkCommand,
 	UpdateBookmarkCommand,
 } from "@/commands/scene";
+import type { MediaTime } from "@/wasm";
 
 export class ScenesManager {
 	private active: TScene | null = null;
@@ -106,12 +107,12 @@ export class ScenesManager {
 		this.notify();
 	}
 
-	async toggleBookmark({ time }: { time: number }): Promise<void> {
+	async toggleBookmark({ time }: { time: MediaTime }): Promise<void> {
 		const command = new ToggleBookmarkCommand(time);
 		this.editor.command.execute({ command });
 	}
 
-	isBookmarked({ time }: { time: number }): boolean {
+	isBookmarked({ time }: { time: MediaTime }): boolean {
 		const activeScene = this.getActiveScene();
 		const activeProject = this.editor.project.getActive();
 
@@ -125,7 +126,7 @@ export class ScenesManager {
 		return isBookmarkAtTime({ bookmarks: activeScene.bookmarks, frameTime });
 	}
 
-	async removeBookmark({ time }: { time: number }): Promise<void> {
+	async removeBookmark({ time }: { time: MediaTime }): Promise<void> {
 		const command = new RemoveBookmarkCommand(time);
 		this.editor.command.execute({ command });
 	}
@@ -134,8 +135,8 @@ export class ScenesManager {
 		time,
 		updates,
 	}: {
-		time: number;
-		updates: Partial<{ note: string; color: string; duration: number }>;
+		time: MediaTime;
+		updates: Partial<Omit<Bookmark, "time">>;
 	}): Promise<void> {
 		const command = new UpdateBookmarkCommand(time, updates);
 		this.editor.command.execute({ command });
@@ -145,14 +146,14 @@ export class ScenesManager {
 		fromTime,
 		toTime,
 	}: {
-		fromTime: number;
-		toTime: number;
+		fromTime: MediaTime;
+		toTime: MediaTime;
 	}): Promise<void> {
 		const command = new MoveBookmarkCommand(fromTime, toTime);
 		this.editor.command.execute({ command });
 	}
 
-	getBookmarkAtTime({ time }: { time: number }) {
+	getBookmarkAtTime({ time }: { time: MediaTime }) {
 		const activeScene = this.active;
 		const activeProject = this.editor.project.getActive();
 
diff --git a/apps/web/src/core/managers/timeline-manager.ts b/apps/web/src/core/managers/timeline-manager.ts
index dbc3332b..a1ead6ca 100644
--- a/apps/web/src/core/managers/timeline-manager.ts
+++ b/apps/web/src/core/managers/timeline-manager.ts
@@ -10,6 +10,7 @@ import type {
 } from "@/timeline";
 import { calculateTotalDuration } from "@/timeline";
 import { findTrackInSceneTracks } from "@/timeline/track-element-update";
+import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
 import {
 	canElementBeHidden,
 	canElementHaveAudio,
@@ -95,10 +96,10 @@ export class TimelineManager {
 		pushHistory = true,
 	}: {
 		elementId: string;
-		trimStart: number;
-		trimEnd: number;
-		startTime?: number;
-		duration?: number;
+		trimStart: MediaTime;
+		trimEnd: MediaTime;
+		startTime?: MediaTime;
+		duration?: MediaTime;
 		pushHistory?: boolean;
 	}): void {
 		const trackId = this.findTrackIdForElement({ elementId });
@@ -188,7 +189,7 @@ export class TimelineManager {
 		retainSide = "both",
 	}: {
 		elements: { trackId: string; elementId: string }[];
-		splitTime: number;
+		splitTime: MediaTime;
 		retainSide?: "both" | "left" | "right";
 	}): { trackId: string; elementId: string }[] {
 		const command = new SplitElementsCommand({
@@ -200,20 +201,20 @@ export class TimelineManager {
 		return command.getRightSideElements();
 	}
 
-	getTotalDuration(): number {
+	getTotalDuration(): MediaTime {
 		const activeScene = this.editor.scenes.getActiveSceneOrNull();
 		if (!activeScene) {
-			return 0;
+			return ZERO_MEDIA_TIME;
 		}
 
 		return calculateTotalDuration({ tracks: activeScene.tracks });
 	}
 
-	getLastFrameTime(): number {
+	getLastFrameTime(): MediaTime {
 		const duration = this.getTotalDuration();
 		const fps = this.editor.project.getActive()?.settings.fps;
 		if (!fps || duration <= 0) return duration;
-		return lastFrameTime({ duration, rate: fps }) ?? duration;
+		return (lastFrameTime({ duration, rate: fps }) ?? duration) as MediaTime;
 	}
 
 	getTrackById({ trackId }: { trackId: string }): TimelineTrack | null {
@@ -483,7 +484,7 @@ export class TimelineManager {
 			trackId: string;
 			elementId: string;
 			propertyPath: AnimationPath;
-			time: number;
+			time: MediaTime;
 			value: AnimationValue;
 			interpolation?: AnimationInterpolation;
 			keyframeId?: string;
@@ -600,7 +601,7 @@ export class TimelineManager {
 		elementId: string;
 		propertyPath: AnimationPath;
 		keyframeId: string;
-		time: number;
+		time: MediaTime;
 	}): void {
 		const command = new RetimeKeyframeCommand({
 			trackId,
@@ -658,7 +659,7 @@ export class TimelineManager {
 		elementId: string;
 		effectId: string;
 		paramKey: string;
-		time: number;
+		time: MediaTime;
 		value: number;
 		interpolation?: "linear" | "hold";
 		keyframeId?: string;
diff --git a/apps/web/src/graphics/components/graphic-tab.tsx b/apps/web/src/graphics/components/graphic-tab.tsx
index 60599772..549ef4b6 100644
--- a/apps/web/src/graphics/components/graphic-tab.tsx
+++ b/apps/web/src/graphics/components/graphic-tab.tsx
@@ -24,6 +24,7 @@ import { Button } from "@/components/ui/button";
 import { HugeiconsIcon } from "@hugeicons/react";

 import { MinusSignIcon, PlusSignIcon } from "@hugeicons/core-free-icons";

 import { cn } from "@/utils/ui";

+import type { MediaTime } from "@/wasm";

 

 registerDefaultGraphics();

 

@@ -197,10 +198,11 @@ function AnimatedGraphicParamField({
 	isPlayheadWithinElementRange,

 	resolvedParams,

 }: {

+	key?: string;

 	param: ParamDefinition;

 	trackId: string;

 	element: GraphicElement;

-	localTime: number;

+	localTime: MediaTime;

 	isPlayheadWithinElementRange: boolean;

 	resolvedParams: ParamValues;

 }) {

diff --git a/apps/web/src/media/use-paste-media.ts b/apps/web/src/media/use-paste-media.ts
index 3055920e..387b2b9a 100644
--- a/apps/web/src/media/use-paste-media.ts
+++ b/apps/web/src/media/use-paste-media.ts
@@ -7,7 +7,7 @@ import { AddMediaAssetCommand } from "@/commands/media";
 import { InsertElementCommand } from "@/commands/timeline";
 import { BatchCommand } from "@/commands";
 import { DEFAULT_NEW_ELEMENT_DURATION } from "@/timeline/creation";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTimeFromSeconds } from "@/wasm";
 import { isTypableDOMElement } from "@/utils/browser";
 import type { MediaType } from "@/media/types";
 
@@ -75,7 +75,7 @@ export function usePasteMedia() {
 							const assetId = addMediaCmd.getAssetId();
 							const duration =
 								asset.duration != null
-									? Math.round(asset.duration * TICKS_PER_SECOND)
+									? mediaTimeFromSeconds({ seconds: asset.duration })
 									: DEFAULT_NEW_ELEMENT_DURATION;
 							const trackType = asset.type === "audio" ? "audio" : "video";
 
diff --git a/apps/web/src/preview/components/toolbar.tsx b/apps/web/src/preview/components/toolbar.tsx
index b44e42ef..084c5b55 100644
--- a/apps/web/src/preview/components/toolbar.tsx
+++ b/apps/web/src/preview/components/toolbar.tsx
@@ -26,6 +26,7 @@ import { PREVIEW_ZOOM_PRESETS } from "@/preview/zoom";
 import { usePreviewViewport } from "./preview-viewport";
 import { GridPopover } from "./guide-popover";
 import { usePreviewStore } from "@/preview/preview-store";
+import type { MediaTime } from "@/wasm";
 
 export function PreviewToolbar({
 	onToggleFullscreen,
@@ -67,13 +68,13 @@ function TimecodeDisplay() {
 	const editor = useEditor();
 	const totalDuration = useEditor((e) => e.timeline.getTotalDuration());
 	const fps = useEditor((e) => e.project.getActive().settings.fps);
-	const [currentTime, setCurrentTime] = useState(() =>
+	const [currentTime, setCurrentTime] = useState<MediaTime>(() =>
 		editor.playback.getCurrentTime(),
 	);
 
 	useEffect(() => {
 		const handler = (e: Event) =>
-			setCurrentTime((e as CustomEvent<{ time: number }>).detail.time);
+			setCurrentTime((e as CustomEvent<{ time: MediaTime }>).detail.time);
 		window.addEventListener("playback-update", handler);
 		window.addEventListener("playback-seek", handler);
 		return () => {
diff --git a/apps/web/src/project/types.ts b/apps/web/src/project/types.ts
index 42e844f6..dca2d785 100644
--- a/apps/web/src/project/types.ts
+++ b/apps/web/src/project/types.ts
@@ -1,5 +1,6 @@
 import type { FrameRate } from "opencut-wasm";
 import type { TScene } from "@/timeline/types";
+import type { MediaTime } from "@/wasm";
 
 export type TBackground =
 	| {
@@ -20,7 +21,7 @@ export interface TProjectMetadata {
 	id: string;
 	name: string;
 	thumbnail?: string;
-	duration: number;
+	duration: MediaTime;
 	createdAt: Date;
 	updatedAt: Date;
 }
@@ -37,7 +38,7 @@ export interface TProjectSettings {
 export interface TTimelineViewState {
 	zoomLevel: number;
 	scrollLeft: number;
-	playheadTime: number;
+	playheadTime: MediaTime;
 }
 
 export interface TProject {
diff --git a/apps/web/src/rendering/components/blending-tab.tsx b/apps/web/src/rendering/components/blending-tab.tsx
index 3e0db46c..870390bf 100644
--- a/apps/web/src/rendering/components/blending-tab.tsx
+++ b/apps/web/src/rendering/components/blending-tab.tsx
@@ -30,14 +30,15 @@ import { useElementPlayhead } from "@/components/editor/panels/properties/hooks/
 import { resolveOpacityAtTime } from "@/animation";
 import { DEFAULTS } from "@/timeline/defaults";
 import { isPropertyAtDefault } from "./transform-tab";
+import type { MediaTime } from "@/wasm";
 
 type BlendingElement = {
 	id: string;
 	opacity: number;
 	type: ElementType;
 	blendMode?: BlendMode;
-	startTime: number;
-	duration: number;
+	startTime: MediaTime;
+	duration: MediaTime;
 	animations?: ElementAnimations;
 };
 
diff --git a/apps/web/src/services/renderer/resolve.ts b/apps/web/src/services/renderer/resolve.ts
index 5495ba3b..0623b399 100644
--- a/apps/web/src/services/renderer/resolve.ts
+++ b/apps/web/src/services/renderer/resolve.ts
@@ -1,4 +1,4 @@
-import { mediaTimeToSeconds } from "opencut-wasm";
+import { mediaTimeToSeconds, roundMediaTime } from "@/wasm";
 import {
 	getElementLocalTime,
 	resolveColorAtTime,
@@ -204,7 +204,7 @@ async function resolveVideoNode({
 	const frame = await videoCache.getFrameAt({
 		mediaId: node.params.mediaId,
 		file: node.params.file,
-		time: mediaTimeToSeconds({ time: sourceTimeTicks }),
+		time: mediaTimeToSeconds({ time: roundMediaTime({ time: sourceTimeTicks }) }),
 	});
 	if (!frame) {
 		return null;
@@ -421,7 +421,7 @@ async function resolveBackdropSource({
 		const frame = await videoCache.getFrameAt({
 			mediaId: node.params.mediaId,
 			file: node.params.file,
-			time: mediaTimeToSeconds({ time: sourceTimeTicks }),
+			time: mediaTimeToSeconds({ time: roundMediaTime({ time: sourceTimeTicks }) }),
 		});
 		if (!frame) {
 			return null;
diff --git a/apps/web/src/services/storage/migrations/__tests__/v27-to-v28.test.ts b/apps/web/src/services/storage/migrations/__tests__/v27-to-v28.test.ts
new file mode 100644
index 00000000..d467c8a1
--- /dev/null
+++ b/apps/web/src/services/storage/migrations/__tests__/v27-to-v28.test.ts
@@ -0,0 +1,257 @@
+import { describe, expect, test } from "bun:test";
+import { transformProjectV27ToV28 } from "../transformers/v27-to-v28";
+
+describe("V27 to V28 Migration", () => {
+	test("rounds persisted media-time floats back to integer ticks", () => {
+		const result = transformProjectV27ToV28({
+			project: {
+				id: "project-v27-float-time",
+				version: 27,
+				metadata: {
+					id: "project-v27-float-time",
+					name: "Project",
+					duration: 2_152_466.3677130044,
+					createdAt: "2026-01-01T00:00:00.000Z",
+					updatedAt: "2026-01-01T00:00:00.000Z",
+				},
+				settings: {
+					fps: { numerator: 30, denominator: 1 },
+					canvasSize: { width: 1920, height: 1080 },
+					background: { type: "color", color: "#000000" },
+				},
+				timelineViewState: {
+					zoomLevel: 1.25,
+					scrollLeft: 120,
+					playheadTime: 301_234.8,
+				},
+				scenes: [
+					{
+						id: "scene-1",
+						name: "Scene 1",
+						isMain: true,
+						bookmarks: [
+							{
+								time: 120_000.4,
+								duration: 60_000.6,
+								note: "Marker",
+								color: "#ff0000",
+							},
+						],
+						tracks: {
+							main: {
+								id: "main-track",
+								type: "video",
+								name: "Main",
+								muted: false,
+								hidden: false,
+								elements: [
+									{
+										id: "element-1",
+										type: "video",
+										name: "Clip",
+										startTime: 300_000.49,
+										duration: 2_152_466.3677130044,
+										trimStart: 30_000.2,
+										trimEnd: 15_000.7,
+										sourceDuration: 2_197_467.6,
+										mediaId: "media-1",
+										transform: {
+											scaleX: 1,
+											scaleY: 1,
+											position: { x: 0, y: 0 },
+											rotate: 0,
+										},
+										opacity: 1,
+										animations: {
+											channels: {
+												opacity: {
+													kind: "scalar",
+													keys: [
+														{
+															id: "key-1",
+															time: 1_000.6,
+															value: 1,
+															segmentToNext: "bezier",
+															tangentMode: "flat",
+															leftHandle: { dt: -120.6, dv: 0 },
+															rightHandle: { dt: 60.4, dv: 0 },
+														},
+													],
+												},
+											},
+										},
+									},
+								],
+							},
+							overlay: [],
+							audio: [],
+						},
+						createdAt: "2026-01-01T00:00:00.000Z",
+						updatedAt: "2026-01-01T00:00:00.000Z",
+					},
+				],
+			},
+		});
+
+		expect(result.skipped).toBe(false);
+		expect(result.project.version).toBe(28);
+
+		const metadata = result.project.metadata as Record<string, unknown>;
+		expect(metadata.duration).toBe(2_152_466);
+
+		const timelineViewState = result.project.timelineViewState as Record<
+			string,
+			unknown
+		>;
+		expect(timelineViewState.playheadTime).toBe(301_235);
+		expect(timelineViewState.zoomLevel).toBe(1.25);
+		expect(timelineViewState.scrollLeft).toBe(120);
+
+		const scenes = result.project.scenes as Array<Record<string, unknown>>;
+		const scene = scenes[0];
+		expect(scene.bookmarks).toEqual([
+			{
+				time: 120_000,
+				duration: 60_001,
+				note: "Marker",
+				color: "#ff0000",
+			},
+		]);
+
+		const tracks = scene.tracks as Record<string, unknown>;
+		const mainTrack = tracks.main as Record<string, unknown>;
+		const elements = mainTrack.elements as Array<Record<string, unknown>>;
+		const element = elements[0];
+		expect(element.startTime).toBe(300_000);
+		expect(element.duration).toBe(2_152_466);
+		expect(element.trimStart).toBe(30_000);
+		expect(element.trimEnd).toBe(15_001);
+		expect(element.sourceDuration).toBe(2_197_468);
+
+		const animations = element.animations as Record<string, unknown>;
+		const channels = animations.channels as Record<string, Record<string, unknown>>;
+		const opacityChannel = channels.opacity;
+		expect(opacityChannel.keys).toEqual([
+			{
+				id: "key-1",
+				time: 1_001,
+				value: 1,
+				segmentToNext: "bezier",
+				tangentMode: "flat",
+				leftHandle: { dt: -121, dv: 0 },
+				rightHandle: { dt: 60, dv: 0 },
+			},
+		]);
+	});
+
+	test("keeps already-integer media-time values unchanged", () => {
+		const result = transformProjectV27ToV28({
+			project: {
+				id: "project-v27-integer-time",
+				version: 27,
+				metadata: {
+					id: "project-v27-integer-time",
+					name: "Project",
+					duration: 120_000,
+					createdAt: "2026-01-01T00:00:00.000Z",
+					updatedAt: "2026-01-01T00:00:00.000Z",
+				},
+				timelineViewState: {
+					zoomLevel: 2,
+					scrollLeft: 300,
+					playheadTime: 30_000,
+				},
+				scenes: [
+					{
+						id: "scene-1",
+						bookmarks: [{ time: 60_000, duration: 15_000 }],
+						tracks: {
+							main: {
+								id: "main-track",
+								type: "video",
+								name: "Main",
+								muted: false,
+								hidden: false,
+								elements: [
+									{
+										id: "element-1",
+										type: "video",
+										name: "Clip",
+										startTime: 10_000,
+										duration: 20_000,
+										trimStart: 1_000,
+										trimEnd: 2_000,
+										sourceDuration: 23_000,
+										mediaId: "media-1",
+										transform: {
+											scaleX: 1,
+											scaleY: 1,
+											position: { x: 0, y: 0 },
+											rotate: 0,
+										},
+										opacity: 1,
+									},
+								],
+							},
+							overlay: [],
+							audio: [],
+						},
+					},
+				],
+			},
+		});
+
+		expect(result.skipped).toBe(false);
+		expect(result.project.version).toBe(28);
+
+		const metadata = result.project.metadata as Record<string, unknown>;
+		expect(metadata.duration).toBe(120_000);
+
+		const timelineViewState = result.project.timelineViewState as Record<
+			string,
+			unknown
+		>;
+		expect(timelineViewState).toEqual({
+			zoomLevel: 2,
+			scrollLeft: 300,
+			playheadTime: 30_000,
+		});
+
+		const scenes = result.project.scenes as Array<Record<string, unknown>>;
+		const scene = scenes[0];
+		expect(scene.bookmarks).toEqual([{ time: 60_000, duration: 15_000 }]);
+
+		const tracks = scene.tracks as Record<string, unknown>;
+		const mainTrack = tracks.main as Record<string, unknown>;
+		const element = (mainTrack.elements as Array<Record<string, unknown>>)[0];
+		expect(element.startTime).toBe(10_000);
+		expect(element.duration).toBe(20_000);
+		expect(element.trimStart).toBe(1_000);
+		expect(element.trimEnd).toBe(2_000);
+		expect(element.sourceDuration).toBe(23_000);
+	});
+
+	test("skips projects already on v28", () => {
+		const result = transformProjectV27ToV28({
+			project: {
+				id: "project-v28",
+				version: 28,
+			},
+		});
+
+		expect(result.skipped).toBe(true);
+		expect(result.reason).toBe("already v28");
+	});
+
+	test("skips projects not on v27", () => {
+		const result = transformProjectV27ToV28({
+			project: {
+				id: "project-v26",
+				version: 26,
+			},
+		});
+
+		expect(result.skipped).toBe(true);
+		expect(result.reason).toBe("not v27");
+	});
+});
diff --git a/apps/web/src/services/storage/migrations/index.ts b/apps/web/src/services/storage/migrations/index.ts
index b290b713..150da7c4 100644
--- a/apps/web/src/services/storage/migrations/index.ts
+++ b/apps/web/src/services/storage/migrations/index.ts
@@ -26,10 +26,11 @@ import { V23toV24Migration } from "./v23-to-v24";
 import { V24toV25Migration } from "./v24-to-v25";
 import { V25toV26Migration } from "./v25-to-v26";
 import { V26toV27Migration } from "./v26-to-v27";
+import { V27toV28Migration } from "./v27-to-v28";
 export { runStorageMigrations } from "./runner";
 export type { MigrationProgress } from "./runner";
 
-export const CURRENT_PROJECT_VERSION = 27;
+export const CURRENT_PROJECT_VERSION = 28;
 
 export const migrations = [
 	new V0toV1Migration(),
@@ -59,4 +60,5 @@ export const migrations = [
 	new V24toV25Migration(),
 	new V25toV26Migration(),
 	new V26toV27Migration(),
+	new V27toV28Migration(),
 ];
diff --git a/apps/web/src/services/storage/migrations/transformers/v27-to-v28.ts b/apps/web/src/services/storage/migrations/transformers/v27-to-v28.ts
new file mode 100644
index 00000000..fc8d8432
--- /dev/null
+++ b/apps/web/src/services/storage/migrations/transformers/v27-to-v28.ts
@@ -0,0 +1,228 @@
+import { roundMediaTime } from "@/wasm";
+import type { MigrationResult, ProjectRecord } from "./types";
+import { getProjectId, isRecord } from "./utils";
+
+export function transformProjectV27ToV28({
+	project,
+}: {
+	project: ProjectRecord;
+}): MigrationResult<ProjectRecord> {
+	if (!getProjectId({ project })) {
+		return { project, skipped: true, reason: "no project id" };
+	}
+
+	const version = project.version;
+	if (typeof version !== "number") {
+		return { project, skipped: true, reason: "invalid version" };
+	}
+	if (version >= 28) {
+		return { project, skipped: true, reason: "already v28" };
+	}
+	if (version !== 27) {
+		return { project, skipped: true, reason: "not v27" };
+	}
+
+	return {
+		project: {
+			...migrateProject({ project }),
+			version: 28,
+		},
+		skipped: false,
+	};
+}
+
+function migrateProject({
+	project,
+}: {
+	project: ProjectRecord;
+}): ProjectRecord {
+	const nextProject = { ...project };
+
+	if (isRecord(project.metadata)) {
+		nextProject.metadata = migrateTimeFields({
+			record: project.metadata,
+			keys: ["duration"],
+		});
+	}
+
+	if (isRecord(project.timelineViewState)) {
+		nextProject.timelineViewState = migrateTimeFields({
+			record: project.timelineViewState,
+			keys: ["playheadTime"],
+		});
+	}
+
+	if (Array.isArray(project.scenes)) {
+		nextProject.scenes = project.scenes.map((scene) => migrateScene({ scene }));
+	}
+
+	return nextProject;
+}
+
+function migrateScene({ scene }: { scene: unknown }): unknown {
+	if (!isRecord(scene)) {
+		return scene;
+	}
+
+	const nextScene = { ...scene };
+
+	if (Array.isArray(scene.bookmarks)) {
+		nextScene.bookmarks = scene.bookmarks.map((bookmark) =>
+			migrateBookmark({ bookmark }),
+		);
+	}
+
+	if (isRecord(scene.tracks)) {
+		nextScene.tracks = migrateTracks({ tracks: scene.tracks });
+	}
+
+	return nextScene;
+}
+
+function migrateTracks({ tracks }: { tracks: ProjectRecord }): ProjectRecord {
+	const nextTracks = { ...tracks };
+
+	if (isRecord(tracks.main)) {
+		nextTracks.main = migrateTrack({ track: tracks.main });
+	}
+
+	if (Array.isArray(tracks.overlay)) {
+		nextTracks.overlay = tracks.overlay.map((track) => migrateTrack({ track }));
+	}
+
+	if (Array.isArray(tracks.audio)) {
+		nextTracks.audio = tracks.audio.map((track) => migrateTrack({ track }));
+	}
+
+	return nextTracks;
+}
+
+function migrateTrack({ track }: { track: unknown }): unknown {
+	if (!isRecord(track) || !Array.isArray(track.elements)) {
+		return track;
+	}
+
+	return {
+		...track,
+		elements: track.elements.map((element) => migrateElement({ element })),
+	};
+}
+
+function migrateElement({ element }: { element: unknown }): unknown {
+	if (!isRecord(element)) {
+		return element;
+	}
+
+	const nextElement = migrateTimeFields({
+		record: element,
+		keys: ["duration", "startTime", "trimStart", "trimEnd", "sourceDuration"],
+	});
+
+	if (isRecord(element.animations)) {
+		nextElement.animations = migrateAnimations({
+			animations: element.animations,
+		});
+	}
+
+	return nextElement;
+}
+
+function migrateAnimations({
+	animations,
+}: {
+	animations: ProjectRecord;
+}): ProjectRecord {
+	if (!isRecord(animations.channels)) {
+		return animations;
+	}
+
+	return {
+		...animations,
+		channels: Object.fromEntries(
+			Object.entries(animations.channels).map(([channelId, channel]) => [
+				channelId,
+				migrateAnimationChannel({ channel }),
+			]),
+		),
+	};
+}
+
+function migrateAnimationChannel({ channel }: { channel: unknown }): unknown {
+	if (!isRecord(channel) || !Array.isArray(channel.keys)) {
+		return channel;
+	}
+
+	return {
+		...channel,
+		keys: channel.keys.map((keyframe) => migrateAnimationKeyframe({ keyframe })),
+	};
+}
+
+function migrateAnimationKeyframe({
+	keyframe,
+}: {
+	keyframe: unknown;
+}): unknown {
+	if (!isRecord(keyframe)) {
+		return keyframe;
+	}
+
+	const nextKeyframe = migrateTimeFields({
+		record: keyframe,
+		keys: ["time"],
+	});
+
+	if (isRecord(keyframe.leftHandle)) {
+		nextKeyframe.leftHandle = migrateTimeFields({
+			record: keyframe.leftHandle,
+			keys: ["dt"],
+		});
+	}
+
+	if (isRecord(keyframe.rightHandle)) {
+		nextKeyframe.rightHandle = migrateTimeFields({
+			record: keyframe.rightHandle,
+			keys: ["dt"],
+		});
+	}
+
+	return nextKeyframe;
+}
+
+function migrateBookmark({ bookmark }: { bookmark: unknown }): unknown {
+	if (!isRecord(bookmark)) {
+		return bookmark;
+	}
+
+	return migrateTimeFields({
+		record: bookmark,
+		keys: ["time", "duration"],
+	});
+}
+
+function migrateTimeFields({
+	record,
+	keys,
+}: {
+	record: ProjectRecord;
+	keys: string[];
+}): ProjectRecord {
+	const nextRecord = { ...record };
+
+	for (const key of keys) {
+		if (!(key in record)) {
+			continue;
+		}
+
+		nextRecord[key] = normalizeMediaTimeValue({ value: record[key] });
+	}
+
+	return nextRecord;
+}
+
+function normalizeMediaTimeValue({ value }: { value: unknown }): unknown {
+	if (typeof value !== "number" || !Number.isFinite(value)) {
+		return value;
+	}
+	return roundMediaTime({ time: value });
+}
diff --git a/apps/web/src/services/storage/migrations/v27-to-v28.ts b/apps/web/src/services/storage/migrations/v27-to-v28.ts
new file mode 100644
index 00000000..aaec6256
--- /dev/null
+++ b/apps/web/src/services/storage/migrations/v27-to-v28.ts
@@ -0,0 +1,14 @@
+import { StorageMigration, type StorageMigrationRunArgs } from "./base";
+import type { MigrationResult, ProjectRecord } from "./transformers/types";
+import { transformProjectV27ToV28 } from "./transformers/v27-to-v28";
+
+export class V27toV28Migration extends StorageMigration {
+	from = 27;
+	to = 28;
+
+	async run({
+		project,
+	}: StorageMigrationRunArgs): Promise<MigrationResult<ProjectRecord>> {
+		return transformProjectV27ToV28({ project });
+	}
+}
diff --git a/apps/web/src/services/storage/service.ts b/apps/web/src/services/storage/service.ts
index 858198eb..a388e807 100644
--- a/apps/web/src/services/storage/service.ts
+++ b/apps/web/src/services/storage/service.ts
@@ -22,12 +22,15 @@ import {
 	runStorageMigrations,
 } from "@/services/storage/migrations";
 import type { Bookmark, SceneTracks, TScene } from "@/timeline";
+import { roundMediaTime } from "@/wasm";
 
 function normalizeBookmarks({ raw }: { raw: unknown }): Bookmark[] {
 	if (!Array.isArray(raw)) return [];
 	return raw
 		.map((item): Bookmark | null => {
-			if (typeof item === "number") return { time: item };
+			if (typeof item === "number") {
+				return { time: roundMediaTime({ time: item }) };
+			}
 			const obj = item as Record<string, unknown>;
 			if (
 				typeof obj !== "object" ||
@@ -37,10 +40,12 @@ function normalizeBookmarks({ raw }: { raw: unknown }): Bookmark[] {
 				return null;
 			}
 			return {
-				time: obj.time,
+				time: roundMediaTime({ time: obj.time }),
 				...(typeof obj.note === "string" && { note: obj.note }),
 				...(typeof obj.color === "string" && { color: obj.color }),
-				...(typeof obj.duration === "number" && { duration: obj.duration }),
+				...(typeof obj.duration === "number" && {
+					duration: roundMediaTime({ time: obj.duration }),
+				}),
 			};
 		})
 		.filter((b): b is Bookmark => b !== null);
@@ -198,9 +203,11 @@ class StorageService {
 				id: serializedProject.metadata.id,
 				name: serializedProject.metadata.name,
 				thumbnail: serializedProject.metadata.thumbnail,
-				duration:
-					serializedProject.metadata.duration ??
-					getProjectDurationFromScenes({ scenes }),
+				duration: roundMediaTime({
+					time:
+						serializedProject.metadata.duration ??
+						getProjectDurationFromScenes({ scenes }),
+				}),
 				createdAt: new Date(serializedProject.metadata.createdAt),
 				updatedAt: new Date(serializedProject.metadata.updatedAt),
 			},
@@ -253,11 +260,13 @@ class StorageService {
 				id: serializedProject.metadata.id,
 				name: serializedProject.metadata.name,
 				thumbnail: serializedProject.metadata.thumbnail,
-				duration:
-					serializedProject.metadata.duration ??
-					getProjectDurationFromScenes({
-						scenes: (serializedProject.scenes ?? []) as unknown as TScene[],
-					}),
+				duration: roundMediaTime({
+					time:
+						serializedProject.metadata.duration ??
+						getProjectDurationFromScenes({
+							scenes: (serializedProject.scenes ?? []) as unknown as TScene[],
+						}),
+				}),
 				createdAt: new Date(serializedProject.metadata.createdAt),
 				updatedAt: new Date(serializedProject.metadata.updatedAt),
 			});
diff --git a/apps/web/src/subtitles/build-subtitle-text-element.ts b/apps/web/src/subtitles/build-subtitle-text-element.ts
index c4ac21ac..4e0bdb85 100644
--- a/apps/web/src/subtitles/build-subtitle-text-element.ts
+++ b/apps/web/src/subtitles/build-subtitle-text-element.ts
@@ -5,7 +5,7 @@ import {
 	setCanvasLetterSpacing,
 } from "@/text/layout";
 import { DEFAULTS } from "@/timeline/defaults";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTimeFromSeconds } from "@/wasm";
 import type { CreateTextElement } from "@/timeline";
 import type { SubtitleCue, SubtitleStyleOverrides } from "./types";
 
@@ -310,8 +310,8 @@ export function buildSubtitleTextElement({
 		...DEFAULTS.text.element,
 		name: `Caption ${index + 1}`,
 		content,
-		duration: Math.round(caption.duration * TICKS_PER_SECOND),
-		startTime: Math.round(caption.startTime * TICKS_PER_SECOND),
+		duration: mediaTimeFromSeconds({ seconds: caption.duration }),
+		startTime: mediaTimeFromSeconds({ seconds: caption.startTime }),
 		fontSize: style.fontSize,
 		fontFamily: style.fontFamily,
 		color: style.color,
diff --git a/apps/web/src/text/components/assets-view.tsx b/apps/web/src/text/components/assets-view.tsx
index 25a49893..ffabe3b8 100644
--- a/apps/web/src/text/components/assets-view.tsx
+++ b/apps/web/src/text/components/assets-view.tsx
@@ -3,11 +3,12 @@ import { PanelView } from "@/components/editor/panels/assets/views/base-panel";
 import { useEditor } from "@/editor/use-editor";

 import { DEFAULTS } from "@/timeline/defaults";

 import { buildTextElement } from "@/timeline/element-utils";

+import type { MediaTime } from "@/wasm";

 

 export function TextView() {

 	const editor = useEditor();

 

-	const handleAddToTimeline = ({ currentTime }: { currentTime: number }) => {

+	const handleAddToTimeline = ({ currentTime }: { currentTime: MediaTime }) => {

 		const activeScene = editor.scenes.getActiveScene();

 		if (!activeScene) return;

 

diff --git a/apps/web/src/timeline/__tests__/update-pipeline.test.ts b/apps/web/src/timeline/__tests__/update-pipeline.test.ts
new file mode 100644
index 00000000..94b32ced
--- /dev/null
+++ b/apps/web/src/timeline/__tests__/update-pipeline.test.ts
@@ -0,0 +1,66 @@
+import { describe, expect, test } from "bun:test";

+import type { Transform } from "@/rendering";

+import type { SceneTracks, VideoElement } from "@/timeline";

+import { applyElementUpdate } from "@/timeline/update-pipeline";

+import { mediaTime, ZERO_MEDIA_TIME } from "@/wasm";

+

+function buildTransform(): Transform {

+	return {

+		scaleX: 1,

+		scaleY: 1,

+		position: { x: 0, y: 0 },

+		rotate: 0,

+	};

+}

+

+function buildVideoElement(overrides: Partial<VideoElement> = {}): VideoElement {

+	return {

+		id: "video-1",

+		type: "video",

+		name: "Video 1",

+		startTime: ZERO_MEDIA_TIME,

+		duration: mediaTime({ ticks: 10 }),

+		trimStart: ZERO_MEDIA_TIME,

+		trimEnd: ZERO_MEDIA_TIME,

+		mediaId: "media-1",

+		transform: buildTransform(),

+		opacity: 1,

+		...overrides,

+	};

+}

+

+function buildTracks(element: VideoElement): SceneTracks {

+	return {

+		overlay: [],

+		main: {

+			id: "main-track",

+			type: "video",

+			name: "Main",

+			muted: false,

+			hidden: false,

+			elements: [element],

+		},

+		audio: [],

+	};

+}

+

+describe("applyElementUpdate", () => {

+	test("rounds retimed durations back to integer media time", () => {

+		const element = buildVideoElement();

+		const tracks = buildTracks(element);

+

+		const updatedElement = applyElementUpdate({

+			element,

+			patch: {

+				retime: { rate: 1.5 },

+			},

+			context: {

+				tracks,

+				trackId: tracks.main.id,

+			},

+		});

+

+		expect(updatedElement.duration).toBe(7);

+		expect(Number.isInteger(updatedElement.duration)).toBe(true);

+	});

+});

diff --git a/apps/web/src/timeline/bookmarks/components/bookmarks.tsx b/apps/web/src/timeline/bookmarks/components/bookmarks.tsx
index 20e22c57..0f0710cb 100644
--- a/apps/web/src/timeline/bookmarks/components/bookmarks.tsx
+++ b/apps/web/src/timeline/bookmarks/components/bookmarks.tsx
@@ -26,6 +26,13 @@ import { Label } from "@/components/ui/label";
 import { uppercase } from "@/utils/string";
 import { clamp, formatNumberForDisplay } from "@/utils/math";
 import { timelineTimeToPixels, timelineTimeToSnappedPixels } from "@/timeline";
+import {
+	type MediaTime,
+	mediaTimeFromSeconds,
+	mediaTimeToSeconds,
+	subMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 const MIN_BOOKMARK_WIDTH_PX = 2;
 const BOOKMARK_MARKER_WIDTH_PX = 12;
@@ -39,12 +46,12 @@ function seekToBookmarkTime({
 	time,
 }: {
 	editor: EditorCore;
-	time: number;
+	time: MediaTime;
 }) {
 	const activeProject = editor.project.getActive();
 	const duration = editor.timeline.getTotalDuration();
 	const rate = activeProject?.settings.fps ?? DEFAULT_FPS;
-	const snappedTime = snappedSeekTime({ time, duration, rate }) ?? time;
+	const snappedTime = (snappedSeekTime({ time, duration, rate }) ?? time) as MediaTime;
 	editor.playback.seek({ time: snappedTime });
 }
 
@@ -137,7 +144,7 @@ function TimelineBookmark({
 
 	const displayTime = isDragging ? dragState.currentTime : bookmark.time;
 	const time = bookmark.time;
-	const bookmarkDuration = bookmark.duration ?? 0;
+	const bookmarkDuration = bookmark.duration ?? ZERO_MEDIA_TIME;
 	const durationWidth =
 		bookmarkDuration > 0
 			? timelineTimeToPixels({ time: bookmarkDuration, zoomLevel })
@@ -182,7 +189,7 @@ function TimelineBookmark({
 						left: `${bookmarkLeft}px`,
 						width: `${bookmarkWidth}px`,
 					}}
-					aria-label={`Bookmark at ${formatNumberForDisplay({ value: time, fractionDigits: 1 })}s`}
+					aria-label={`Bookmark at ${formatNumberForDisplay({ value: mediaTimeToSeconds({ time }), fractionDigits: 1 })}s`}
 					type="button"
 					onMouseDown={handleMouseDown}
 					onClick={handleClick}
@@ -286,8 +293,8 @@ function BookmarkPopoverContent({
 	onPopoverClose,
 }: {
 	bookmark: Bookmark;
-	time: number;
-	timelineDuration: number;
+	time: MediaTime;
+	timelineDuration: MediaTime;
 	onPopoverClose: () => void;
 }) {
 	const editor = useEditor();
@@ -314,9 +321,8 @@ function BookmarkPopoverContent({
 		note,
 		color,
 		duration,
-	}: Partial<{ note: string; color: string; duration: number }>) => {
-		const updates: Partial<{ note: string; color: string; duration: number }> =
-			{};
+	}: Partial<Omit<Bookmark, "time">>) => {
+		const updates: Partial<Omit<Bookmark, "time">> = {};
 		if (note !== undefined && note !== bookmark.note) updates.note = note;
 		if (
 			color !== undefined &&
@@ -330,6 +336,15 @@ function BookmarkPopoverContent({
 		if (Object.keys(updates).length === 0) return;
 		editor.scenes.updateBookmark({ time, updates });
 	};
+	const maxDuration = mediaTimeToSeconds({
+		time:
+			timelineDuration > time
+				? subMediaTime({ a: timelineDuration, b: time })
+				: ZERO_MEDIA_TIME,
+	});
+	const durationSeconds = mediaTimeToSeconds({
+		time: bookmark.duration ?? ZERO_MEDIA_TIME,
+	});
 
 	return (
 		<>
@@ -387,7 +402,7 @@ function BookmarkPopoverContent({
 						type="number"
 						min={0}
 						step={0.1}
-						value={bookmark.duration ?? 0}
+						value={durationSeconds}
 						onChange={(event) => {
 							const parsed = parseFloat(event.target.value);
 							const value = Number.isNaN(parsed)
@@ -395,9 +410,11 @@ function BookmarkPopoverContent({
 								: clamp({
 										value: parsed,
 										min: 0,
-										max: Math.max(0, timelineDuration - time),
+										max: maxDuration,
 									});
-							handleUpdate({ duration: value });
+							handleUpdate({
+								duration: mediaTimeFromSeconds({ seconds: value }),
+							});
 						}}
 						className="h-8 text-sm"
 						containerClassName="w-full"
diff --git a/apps/web/src/timeline/bookmarks/hooks/use-bookmark-drag.ts b/apps/web/src/timeline/bookmarks/hooks/use-bookmark-drag.ts
index 1071c6dd..8996330b 100644
--- a/apps/web/src/timeline/bookmarks/hooks/use-bookmark-drag.ts
+++ b/apps/web/src/timeline/bookmarks/hooks/use-bookmark-drag.ts
@@ -21,15 +21,16 @@ import { getElementEdgeSnapPoints } from "@/timeline/element-snap-source";
 import { getPlayheadSnapPoints } from "@/timeline/playhead-snap-source";
 import { getAnimationKeyframeSnapPointsForTimeline } from "@/animation/timeline-snap-points";
 import type { Bookmark } from "@/timeline";
+import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
 
 export interface BookmarkDragState {
 	isDragging: boolean;
-	bookmarkTime: number | null;
-	currentTime: number;
+	bookmarkTime: MediaTime | null;
+	currentTime: MediaTime;
 }
 
 interface PendingBookmarkDrag {
-	bookmarkTime: number;
+	bookmarkTime: MediaTime;
 	startMouseX: number;
 	startMouseY: number;
 }
@@ -58,7 +59,7 @@ export function useBookmarkDrag({
 	const [dragState, setDragState] = useState<BookmarkDragState>({
 		isDragging: false,
 		bookmarkTime: null,
-		currentTime: 0,
+		currentTime: ZERO_MEDIA_TIME,
 	});
 	const [isPendingDrag, setIsPendingDrag] = useState(false);
 	const pendingDragRef = useRef<PendingBookmarkDrag | null>(null);
@@ -69,8 +70,8 @@ export function useBookmarkDrag({
 			bookmarkTime,
 			initialCurrentTime,
 		}: {
-			bookmarkTime: number;
-			initialCurrentTime: number;
+			bookmarkTime: MediaTime;
+			initialCurrentTime: MediaTime;
 		}) => {
 			setDragState({
 				isDragging: true,
@@ -85,7 +86,7 @@ export function useBookmarkDrag({
 		setDragState({
 			isDragging: false,
 			bookmarkTime: null,
-			currentTime: 0,
+			currentTime: ZERO_MEDIA_TIME,
 		});
 	}, []);
 
@@ -94,9 +95,9 @@ export function useBookmarkDrag({
 			rawTime,
 			excludeBookmarkTime,
 		}: {
-			rawTime: number;
-			excludeBookmarkTime: number;
-		}): { snappedTime: number; snapPoint: SnapPoint | null } => {
+			rawTime: MediaTime;
+			excludeBookmarkTime: MediaTime;
+		}): { snappedTime: MediaTime; snapPoint: SnapPoint | null } => {
 			const shouldSnap = snappingEnabled && !isShiftHeldRef.current;
 			if (!shouldSnap) {
 				return { snappedTime: rawTime, snapPoint: null };
@@ -116,7 +117,7 @@ export function useBookmarkDrag({
 				maxSnapDistance: getTimelineSnapThresholdInTicks({ zoomLevel }),
 			});
 			return {
-				snappedTime: result.snappedTime,
+				snappedTime: result.snappedTime as MediaTime,
 				snapPoint: result.snapPoint,
 			};
 		},
@@ -162,11 +163,14 @@ export function useBookmarkDrag({
 					zoomLevel,
 					scrollLeft,
 				});
-				const frameSnappedTime =
+				const clampedTime =
+					mouseTime > duration ? duration : mouseTime;
+				const frameSnappedTime = (
 					roundToFrame({
-						time: Math.max(0, Math.min(mouseTime, duration)),
+						time: clampedTime,
 						rate: activeProject.settings.fps,
-					}) ?? Math.max(0, Math.min(mouseTime, duration));
+					}) ?? clampedTime
+				) as MediaTime;
 				const { snappedTime: initialTime } = getSnapResult({
 					rawTime: frameSnappedTime,
 					excludeBookmarkTime: bookmarkTime,
@@ -193,10 +197,12 @@ export function useBookmarkDrag({
 				zoomLevel,
 				scrollLeft,
 			});
-			const clampedTime = Math.max(0, Math.min(mouseTime, duration));
-			const frameSnappedTime =
+			const clampedTime =
+				mouseTime > duration ? duration : mouseTime;
+			const frameSnappedTime = (
 				roundToFrame({ time: clampedTime, rate: activeProject.settings.fps }) ??
-				clampedTime;
+				clampedTime
+			) as MediaTime;
 			const snapResult = getSnapResult({
 				rawTime: frameSnappedTime,
 				excludeBookmarkTime: dragState.bookmarkTime,
@@ -234,10 +240,8 @@ export function useBookmarkDrag({
 				return;
 			}
 
-			const clampedTime = Math.max(
-				0,
-				Math.min(dragState.currentTime, duration),
-			);
+			const clampedTime =
+				dragState.currentTime > duration ? duration : dragState.currentTime;
 
 			editor.scenes.moveBookmark({
 				fromTime: dragState.bookmarkTime,
diff --git a/apps/web/src/timeline/bookmarks/preview-overlay-source.tsx b/apps/web/src/timeline/bookmarks/preview-overlay-source.tsx
index 8e2b4bcf..2c254c84 100644
--- a/apps/web/src/timeline/bookmarks/preview-overlay-source.tsx
+++ b/apps/web/src/timeline/bookmarks/preview-overlay-source.tsx
@@ -5,6 +5,7 @@ import {
 	type PreviewOverlaySourceResult,
 } from "@/preview/overlays";
 import { getBookmarksActiveAtTime } from "./utils";
+import type { MediaTime } from "@/wasm";
 
 export const bookmarkNotesPreviewOverlay: PreviewOverlayDefinition = {
 	id: "bookmark-notes",
@@ -15,7 +16,7 @@ export const bookmarkNotesPreviewOverlay: PreviewOverlayDefinition = {
 function BookmarkNotesOverlay({
 	bookmarks,
 }: {
-	bookmarks: Array<{ time: number; note: string; color?: string }>;
+	bookmarks: Array<{ time: MediaTime; note: string; color?: string }>;
 }) {
 	return (
 		<div className="flex flex-col gap-1.5" aria-live="polite">
@@ -43,7 +44,7 @@ export function getBookmarkPreviewOverlaySource({
 	isVisible,
 }: {
 	bookmarks: Bookmark[];
-	time: number;
+	time: MediaTime;
 	isVisible: boolean;
 }): PreviewOverlaySourceResult {
 	const bookmarksWithNotes = getBookmarksActiveAtTime({
diff --git a/apps/web/src/timeline/bookmarks/utils.ts b/apps/web/src/timeline/bookmarks/utils.ts
index d05fe3a9..52e5aa60 100644
--- a/apps/web/src/timeline/bookmarks/utils.ts
+++ b/apps/web/src/timeline/bookmarks/utils.ts
@@ -1,13 +1,14 @@
 import type { Bookmark } from "@/timeline";
 import type { FrameRate } from "opencut-wasm";
 import { roundToFrame } from "opencut-wasm";
+import { addMediaTime, type MediaTime } from "@/wasm";
 
 function bookmarkTimeEqual({
 	bookmarkTime,
 	frameTime,
 }: {
-	bookmarkTime: number;
-	frameTime: number;
+	bookmarkTime: MediaTime;
+	frameTime: MediaTime;
 }): boolean {
 	return bookmarkTime === frameTime;
 }
@@ -17,7 +18,7 @@ export function findBookmarkIndex({
 	frameTime,
 }: {
 	bookmarks: Bookmark[];
-	frameTime: number;
+	frameTime: MediaTime;
 }): number {
 	return bookmarks.findIndex((bookmark) =>
 		bookmarkTimeEqual({ bookmarkTime: bookmark.time, frameTime }),
@@ -29,7 +30,7 @@ export function isBookmarkAtTime({
 	frameTime,
 }: {
 	bookmarks: Bookmark[];
-	frameTime: number;
+	frameTime: MediaTime;
 }): boolean {
 	return bookmarks.some((bookmark) =>
 		bookmarkTimeEqual({ bookmarkTime: bookmark.time, frameTime }),
@@ -41,7 +42,7 @@ export function toggleBookmarkInArray({
 	frameTime,
 }: {
 	bookmarks: Bookmark[];
-	frameTime: number;
+	frameTime: MediaTime;
 }): Bookmark[] {
 	const bookmarkIndex = findBookmarkIndex({ bookmarks, frameTime });
 
@@ -58,7 +59,7 @@ export function removeBookmarkFromArray({
 	frameTime,
 }: {
 	bookmarks: Bookmark[];
-	frameTime: number;
+	frameTime: MediaTime;
 }): Bookmark[] {
 	return bookmarks.filter(
 		(bookmark) =>
@@ -72,7 +73,7 @@ export function updateBookmarkInArray({
 	updates,
 }: {
 	bookmarks: Bookmark[];
-	frameTime: number;
+	frameTime: MediaTime;
 	updates: Partial<Omit<Bookmark, "time">>;
 }): Bookmark[] {
 	const index = findBookmarkIndex({ bookmarks, frameTime });
@@ -92,8 +93,8 @@ export function moveBookmarkInArray({
 	toTime,
 }: {
 	bookmarks: Bookmark[];
-	fromTime: number;
-	toTime: number;
+	fromTime: MediaTime;
+	toTime: MediaTime;
 }): Bookmark[] {
 	const index = findBookmarkIndex({ bookmarks, frameTime: fromTime });
 	if (index === -1) {
@@ -110,10 +111,10 @@ export function getFrameTime({
 	time,
 	fps,
 }: {
-	time: number;
+	time: MediaTime;
 	fps: FrameRate;
-}): number {
-	return roundToFrame({ time, rate: fps }) ?? time;
+}): MediaTime {
+	return (roundToFrame({ time, rate: fps }) ?? time) as MediaTime;
 }
 
 export function getBookmarkAtTime({
@@ -121,7 +122,7 @@ export function getBookmarkAtTime({
 	frameTime,
 }: {
 	bookmarks: Bookmark[];
-	frameTime: number;
+	frameTime: MediaTime;
 }): Bookmark | null {
 	const index = findBookmarkIndex({ bookmarks, frameTime });
 	return index === -1 ? null : bookmarks[index];
@@ -132,13 +133,13 @@ export function getBookmarksActiveAtTime({
 	time,
 }: {
 	bookmarks: Bookmark[];
-	time: number;
+	time: MediaTime;
 }): Bookmark[] {
 	return bookmarks.filter((bookmark) => {
 		const start = bookmark.time;
 		const end =
 			bookmark.duration != null && bookmark.duration > 0
-				? start + bookmark.duration
+				? addMediaTime({ a: start, b: bookmark.duration })
 				: start;
 		return time >= start && time <= end;
 	});
diff --git a/apps/web/src/timeline/components/drop-target.ts b/apps/web/src/timeline/components/drop-target.ts
index be2495e4..f68a4b72 100644
--- a/apps/web/src/timeline/components/drop-target.ts
+++ b/apps/web/src/timeline/components/drop-target.ts
@@ -3,7 +3,12 @@ import type { ComputeDropTargetParams, DropTarget } from "@/timeline";
 import { resolveTrackPlacement } from "@/timeline/placement";
 import { TIMELINE_TRACK_GAP_PX } from "./layout";
 import { getTrackHeight } from "./track-layout";
-import { TICKS_PER_SECOND } from "@/wasm";
+import {
+	mediaTime,
+	type MediaTime,
+	roundMediaTime,
+	TICKS_PER_SECOND,
+} from "@/wasm";
 
 function findElementAtPosition({
 	mouseX,
@@ -20,9 +25,11 @@ function findElementAtPosition({
 	pixelsPerSecond: number;
 	zoomLevel: number;
 }): { elementId: string; trackId: string } | null {
-	const time = Math.round(
-		(mouseX / (pixelsPerSecond * zoomLevel)) * TICKS_PER_SECOND,
-	);
+	const time = mediaTime({
+		ticks: Math.round(
+			(mouseX / (pixelsPerSecond * zoomLevel)) * TICKS_PER_SECOND,
+		),
+	});
 	const track = tracks[trackIndex];
 	if (!track || !("elements" in track)) return null;
 
@@ -82,7 +89,7 @@ const EMPTY_TARGET_ELEMENT = null;
 function fallbackNewTrackDropTarget({
 	xPosition,
 }: {
-	xPosition: number;
+	xPosition: MediaTime;
 }): DropTarget {
 	return {
 		trackIndex: 0,
@@ -111,13 +118,16 @@ export function computeDropTarget({
 	const orderedTracks = [...tracks.overlay, tracks.main, ...tracks.audio];
 	const mainTrackIndex = tracks.overlay.length;
 	const xPosition =
-		typeof startTimeOverride === "number"
+		startTimeOverride !== undefined
 			? startTimeOverride
 			: isExternalDrop
 				? playheadTime
-				: Math.round(
-				Math.max(0, mouseX / (pixelsPerSecond * zoomLevel)) * TICKS_PER_SECOND,
-			);
+				: mediaTime({
+						ticks: Math.round(
+							Math.max(0, mouseX / (pixelsPerSecond * zoomLevel)) *
+								TICKS_PER_SECOND,
+						),
+					});
 
 	if (orderedTracks.length === 0) {
 		const placementResult = resolveTrackPlacement({
@@ -221,7 +231,10 @@ export function computeDropTarget({
 	}
 
 	if (placementResult.kind === "existingTrack") {
-		const adjustedXPosition = placementResult.adjustedStartTime ?? xPosition;
+		const adjustedXPosition =
+			placementResult.adjustedStartTime !== undefined
+				? roundMediaTime({ time: placementResult.adjustedStartTime })
+				: xPosition;
 
 		return {
 			trackIndex: placementResult.trackIndex,
diff --git a/apps/web/src/timeline/components/index.tsx b/apps/web/src/timeline/components/index.tsx
index e6a9df49..5d61a0a9 100644
--- a/apps/web/src/timeline/components/index.tsx
+++ b/apps/web/src/timeline/components/index.tsx
@@ -29,6 +29,7 @@ import {
 	useState,
 	type ReactNode,
 } from "react";
+import type { MediaTime } from "@/wasm";
 import type { ElementDragState, DropTarget } from "@/timeline";
 import { TimelineTrackContent } from "./timeline-track";
 import { TimelinePlayhead } from "./timeline-playhead";
@@ -132,7 +133,7 @@ export function Timeline() {
 		[scene],
 	);
 	const mainTrackId = scene?.tracks.main.id ?? null;
-	const seek = (time: number) => editor.playback.seek({ time });
+	const seek = (time: MediaTime) => editor.playback.seek({ time });
 
 	const timelineRef = useRef<HTMLDivElement>(null);
 	const timelineHeaderRef = useRef<HTMLDivElement>(null);
diff --git a/apps/web/src/timeline/components/timeline-element.tsx b/apps/web/src/timeline/components/timeline-element.tsx
index 74c34607..e0eeb378 100644
--- a/apps/web/src/timeline/components/timeline-element.tsx
+++ b/apps/web/src/timeline/components/timeline-element.tsx
@@ -49,7 +49,7 @@ import {
 import { buildWaveformGainSamples } from "@/timeline/audio-state";
 import { getTimelinePixelsPerSecond } from "@/timeline";
 import { buildWaveformSourceKey } from "@/media/waveform-summary";
-import { TICKS_PER_SECOND } from "@/wasm/ticks";
+import { addMediaTime, TICKS_PER_SECOND, ZERO_MEDIA_TIME } from "@/wasm";
 import {
 	getActionDefinition,
 	type TAction,
@@ -257,10 +257,11 @@ export function TimelineElement({
 		isBeingDragged && dragState.isDragging
 			? dragState.currentMouseY - dragState.startMouseY
 			: 0;
-	const dragTimeOffset = dragState.dragTimeOffsets[element.id] ?? 0;
+	const dragTimeOffset =
+		dragState.dragTimeOffsets[element.id] ?? ZERO_MEDIA_TIME;
 	const elementStartTime =
 		isBeingDragged && dragState.isDragging
-			? dragState.currentTime + dragTimeOffset
+			? addMediaTime({ a: dragState.currentTime, b: dragTimeOffset })
 			: renderElement.startTime;
 	const displayedStartTime = elementStartTime;
 	const displayedDuration = renderElement.duration;
diff --git a/apps/web/src/timeline/components/timeline-playhead.tsx b/apps/web/src/timeline/components/timeline-playhead.tsx
index 4dd3329f..5b1e45ab 100644
--- a/apps/web/src/timeline/components/timeline-playhead.tsx
+++ b/apps/web/src/timeline/components/timeline-playhead.tsx
@@ -7,7 +7,14 @@ import {
 	timelineTimeToSnappedPixels,
 } from "@/timeline";
 import { useTimelinePlayhead } from "@/timeline/hooks/use-timeline-playhead";
-import { TICKS_PER_SECOND } from "@/wasm";
+import {
+	addMediaTime,
+	maxMediaTime,
+	mediaTime,
+	subMediaTime,
+	TICKS_PER_SECOND,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 import { useEditor } from "@/editor/use-editor";
 import { TIMELINE_SCROLLBAR_SIZE_PX } from "./layout";
 import { TIMELINE_LAYERS } from "./layers";
@@ -72,17 +79,24 @@ export function TimelinePlayhead({
 
 		event.preventDefault();
 		const fps = editor.project.getActive().settings.fps;
-		const ticksPerFrame = Math.round(
-			(TICKS_PER_SECOND * fps.denominator) / fps.numerator,
-		);
+		const ticksPerFrame = mediaTime({
+			ticks: Math.round(
+				(TICKS_PER_SECOND * fps.denominator) / fps.numerator,
+			),
+		});
 		const direction = event.key === "ArrowRight" ? 1 : -1;
 		const now = editor.playback.getCurrentTime();
-		const nextTime = Math.max(
-			0,
-			Math.min(duration, now + direction * ticksPerFrame),
-		);
+		const nextTime =
+			direction > 0
+				? addMediaTime({ a: now, b: ticksPerFrame })
+				: subMediaTime({ a: now, b: ticksPerFrame });
 
-		editor.playback.seek({ time: nextTime });
+		editor.playback.seek({
+			time: maxMediaTime({
+				a: ZERO_MEDIA_TIME,
+				b: duration < nextTime ? duration : nextTime,
+			}),
+		});
 	};
 
 	return (
diff --git a/apps/web/src/timeline/creation.ts b/apps/web/src/timeline/creation.ts
index 2ac7f246..f3c93b8d 100644
--- a/apps/web/src/timeline/creation.ts
+++ b/apps/web/src/timeline/creation.ts
@@ -1,3 +1,5 @@
-import { TICKS_PER_SECOND } from "@/wasm/ticks";
+import { mediaTime, TICKS_PER_SECOND } from "@/wasm";
 
-export const DEFAULT_NEW_ELEMENT_DURATION = 5 * TICKS_PER_SECOND;
+export const DEFAULT_NEW_ELEMENT_DURATION = mediaTime({
+	ticks: 5 * TICKS_PER_SECOND,
+});
diff --git a/apps/web/src/timeline/defaults.ts b/apps/web/src/timeline/defaults.ts
index 06639e01..3b47b4f4 100644
--- a/apps/web/src/timeline/defaults.ts
+++ b/apps/web/src/timeline/defaults.ts
@@ -1,6 +1,7 @@
 import { DEFAULT_NEW_ELEMENT_DURATION } from "@/timeline/creation";
 import type { TTimelineViewState } from "@/project/types";
 import type { BlendMode, Transform } from "@/rendering";
+import { ZERO_MEDIA_TIME } from "@/wasm";
 import type { TextElement } from "./types";
 
 const defaultTransform: Transform = {
@@ -42,9 +43,9 @@ const defaultTextElement: Omit<TextElement, "id"> = {
 	letterSpacing: defaultTextLetterSpacing,
 	lineHeight: defaultTextLineHeight,
 	duration: DEFAULT_NEW_ELEMENT_DURATION,
-	startTime: 0,
-	trimStart: 0,
-	trimEnd: 0,
+	startTime: ZERO_MEDIA_TIME,
+	trimStart: ZERO_MEDIA_TIME,
+	trimEnd: ZERO_MEDIA_TIME,
 	transform: {
 		...defaultTransform,
 		position: { ...defaultTransform.position },
@@ -55,7 +56,7 @@ const defaultTextElement: Omit<TextElement, "id"> = {
 const defaultTimelineViewState: TTimelineViewState = {
 	zoomLevel: 1,
 	scrollLeft: 0,
-	playheadTime: 0,
+	playheadTime: ZERO_MEDIA_TIME,
 };
 
 export const DEFAULTS = {
diff --git a/apps/web/src/timeline/drag-utils.ts b/apps/web/src/timeline/drag-utils.ts
index a731d7a0..ad8d8001 100644
--- a/apps/web/src/timeline/drag-utils.ts
+++ b/apps/web/src/timeline/drag-utils.ts
@@ -1,5 +1,5 @@
 import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/timeline/scale";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTime, type MediaTime, TICKS_PER_SECOND } from "@/wasm";
 
 export function getMouseTimeFromClientX({
 	clientX,
@@ -11,11 +11,13 @@ export function getMouseTimeFromClientX({
 	containerRect: DOMRect;
 	zoomLevel: number;
 	scrollLeft: number;
-}): number {
+}): MediaTime {
 	const mouseX = clientX - containerRect.left + scrollLeft;
 	const seconds = Math.max(
 		0,
 		mouseX / (BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel),
 	);
-	return Math.round(seconds * TICKS_PER_SECOND);
+	return mediaTime({
+		ticks: Math.round(seconds * TICKS_PER_SECOND),
+	});
 }
diff --git a/apps/web/src/timeline/element-utils.ts b/apps/web/src/timeline/element-utils.ts
index 676bc823..cddbf6fd 100644
--- a/apps/web/src/timeline/element-utils.ts
+++ b/apps/web/src/timeline/element-utils.ts
@@ -29,6 +29,7 @@ import { buildDefaultEffectInstance } from "@/effects";
 import { buildDefaultGraphicInstance } from "@/graphics";
 import type { ParamValues } from "@/params";
 import { capitalizeFirstLetter } from "@/utils/string";
+import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
 
 export function canElementHaveAudio(
 	element: TimelineElement,
@@ -107,7 +108,7 @@ export function buildTextElement({
 	startTime,
 }: {
 	raw: Partial<Omit<TextElement, "type" | "id">>;
-	startTime: number;
+	startTime: MediaTime;
 }): CreateTimelineElement {
 	const t = raw as Partial<TextElement>;
 
@@ -117,8 +118,8 @@ export function buildTextElement({
 		content: t.content ?? DEFAULTS.text.element.content,
 		duration: t.duration ?? DEFAULT_NEW_ELEMENT_DURATION,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		fontSize: t.fontSize ?? DEFAULTS.text.element.fontSize,
 		fontFamily: t.fontFamily ?? DEFAULTS.text.element.fontFamily,
 		color: t.color ?? DEFAULTS.text.element.color,
@@ -141,8 +142,8 @@ export function buildEffectElement({
 	duration,
 }: {
 	effectType: string;
-	startTime: number;
-	duration?: number;
+	startTime: MediaTime;
+	duration?: MediaTime;
 }): CreateEffectElement {
 	const instance = buildDefaultEffectInstance({ effectType });
 	return {
@@ -152,8 +153,8 @@ export function buildEffectElement({
 		params: instance.params,
 		duration: duration ?? DEFAULT_NEW_ELEMENT_DURATION,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 	};
 }
 
@@ -166,7 +167,7 @@ export function buildStickerElement({
 }: {
 	stickerId: string;
 	name?: string;
-	startTime: number;
+	startTime: MediaTime;
 	intrinsicWidth?: number;
 	intrinsicHeight?: number;
 }): CreateStickerElement {
@@ -180,8 +181,8 @@ export function buildStickerElement({
 		intrinsicHeight,
 		duration: DEFAULT_NEW_ELEMENT_DURATION,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		transform: {
 			...DEFAULTS.element.transform,
 			position: { ...DEFAULTS.element.transform.position },
@@ -199,7 +200,7 @@ export function buildGraphicElement({
 }: {
 	definitionId: string;
 	name?: string;
-	startTime: number;
+	startTime: MediaTime;
 	params?: Partial<ParamValues>;
 }): CreateGraphicElement {
 	const instance = buildDefaultGraphicInstance({ definitionId });
@@ -210,8 +211,8 @@ export function buildGraphicElement({
 		params: { ...instance.params, ...(params ?? {}) } as ParamValues,
 		duration: DEFAULT_NEW_ELEMENT_DURATION,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		transform: {
 			...DEFAULTS.element.transform,
 			position: { ...DEFAULTS.element.transform.position },
@@ -229,8 +230,8 @@ function buildVideoElement({
 }: {
 	mediaId: string;
 	name: string;
-	duration: number;
-	startTime: number;
+	duration: MediaTime;
+	startTime: MediaTime;
 }): CreateVideoElement {
 	return {
 		type: "video",
@@ -238,8 +239,8 @@ function buildVideoElement({
 		name,
 		duration,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		sourceDuration: duration,
 		muted: false,
 		isSourceAudioEnabled: true,
@@ -262,8 +263,8 @@ function buildImageElement({
 }: {
 	mediaId: string;
 	name: string;
-	duration: number;
-	startTime: number;
+	duration: MediaTime;
+	startTime: MediaTime;
 }): CreateImageElement {
 	return {
 		type: "image",
@@ -271,8 +272,8 @@ function buildImageElement({
 		name,
 		duration,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		hidden: false,
 		transform: {
 			...DEFAULTS.element.transform,
@@ -292,8 +293,8 @@ function buildUploadAudioElement({
 }: {
 	mediaId: string;
 	name: string;
-	duration: number;
-	startTime: number;
+	duration: MediaTime;
+	startTime: MediaTime;
 	buffer?: AudioBuffer;
 }): CreateUploadAudioElement {
 	const element: CreateUploadAudioElement = {
@@ -303,8 +304,8 @@ function buildUploadAudioElement({
 		name,
 		duration,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		sourceDuration: duration,
 		volume: DEFAULTS.element.volume,
 		muted: false,
@@ -326,8 +327,8 @@ export function buildElementFromMedia({
 	mediaId: string;
 	mediaType: MediaType;
 	name: string;
-	duration: number;
-	startTime: number;
+	duration: MediaTime;
+	startTime: MediaTime;
 	buffer?: AudioBuffer;
 }): CreateTimelineElement {
 	switch (mediaType) {
@@ -355,8 +356,8 @@ export function buildLibraryAudioElement({
 }: {
 	sourceUrl: string;
 	name: string;
-	duration: number;
-	startTime: number;
+	duration: MediaTime;
+	startTime: MediaTime;
 	buffer?: AudioBuffer;
 }): CreateLibraryAudioElement {
 	const element: CreateLibraryAudioElement = {
@@ -366,8 +367,8 @@ export function buildLibraryAudioElement({
 		name,
 		duration,
 		startTime,
-		trimStart: 0,
-		trimEnd: 0,
+		trimStart: ZERO_MEDIA_TIME,
+		trimEnd: ZERO_MEDIA_TIME,
 		sourceDuration: duration,
 		volume: DEFAULTS.element.volume,
 		muted: false,
diff --git a/apps/web/src/timeline/group-move/build-group.ts b/apps/web/src/timeline/group-move/build-group.ts
index 00f39d55..3e19e3e3 100644
--- a/apps/web/src/timeline/group-move/build-group.ts
+++ b/apps/web/src/timeline/group-move/build-group.ts
@@ -2,6 +2,7 @@ import type { ElementRef, SceneTracks } from "@/timeline";
 import { findTrackInSceneTracks } from "@/timeline/track-element-update";
 import type { GroupMember, MoveGroup } from "./types";
 import { getTrackPlacementById } from "./track-placement";
+import { subMediaTime } from "@/wasm";
 
 export function buildMoveGroup({
 	anchorRef,
@@ -59,7 +60,10 @@ export function buildMoveGroup({
 				elementId: element.id,
 				elementType: element.type,
 				duration: element.duration,
-				timeOffset: element.startTime - anchorElement.startTime,
+				timeOffset: subMediaTime({
+					a: element.startTime,
+					b: anchorElement.startTime,
+				}),
 				trackSection: placement.section,
 				sectionIndex: placement.sectionIndex,
 				displayIndex: placement.displayIndex,
diff --git a/apps/web/src/timeline/group-move/resolve-move.ts b/apps/web/src/timeline/group-move/resolve-move.ts
index 60940315..8307aad0 100644
--- a/apps/web/src/timeline/group-move/resolve-move.ts
+++ b/apps/web/src/timeline/group-move/resolve-move.ts
@@ -12,6 +12,13 @@ import {
 	getTrackPlacementByDisplayIndex,
 	getTrackPlacementById,
 } from "./track-placement";
+import {
+	addMediaTime,
+	maxMediaTime,
+	type MediaTime,
+	subMediaTime,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 
 type GroupMoveTarget =
 	| {
@@ -32,7 +39,7 @@ export function resolveGroupMove({
 }: {
 	group: MoveGroup;
 	tracks: SceneTracks;
-	anchorStartTime: number;
+	anchorStartTime: MediaTime;
 	target: GroupMoveTarget;
 }): GroupMoveResult | null {
 	if (target.kind === "newTracks") {
@@ -61,7 +68,7 @@ function resolveExistingTrackMove({
 }: {
 	group: MoveGroup;
 	tracks: SceneTracks;
-	anchorStartTime: number;
+	anchorStartTime: MediaTime;
 	anchorTargetTrackId: string;
 }): GroupMoveResult | null {
 	const anchorTargetPlacement = getTrackPlacementById({
@@ -93,7 +100,10 @@ function resolveExistingTrackMove({
 		targetTrackId:
 			targetTrackIdsByElementId.get(member.elementId) ?? member.trackId,
 		elementId: member.elementId,
-		newStartTime: clampedAnchorStartTime + member.timeOffset,
+		newStartTime: addMediaTime({
+			a: clampedAnchorStartTime,
+			b: member.timeOffset,
+		}),
 	}));
 
 	if (!canApplyMovesToExistingTracks({ tracks, moves })) {
@@ -119,7 +129,7 @@ function resolveNewTrackMove({
 }: {
 	group: MoveGroup;
 	tracks: SceneTracks;
-	anchorStartTime: number;
+	anchorStartTime: MediaTime;
 	anchorInsertIndex: number;
 	newTrackIds: string[];
 }): GroupMoveResult | null {
@@ -173,7 +183,10 @@ function resolveNewTrackMove({
 		sourceTrackId: member.trackId,
 		targetTrackId: newTrackIds[memberIndex],
 		elementId: member.elementId,
-		newStartTime: clampedAnchorStartTime + member.timeOffset,
+		newStartTime: addMediaTime({
+			a: clampedAnchorStartTime,
+			b: member.timeOffset,
+		}),
 	}));
 
 	return {
@@ -335,17 +348,26 @@ function clampAnchorStartTime({
 }: {
 	group: MoveGroup;
 	tracks: SceneTracks;
-	anchorStartTime: number;
+	anchorStartTime: MediaTime;
 	targetTrackIdsByElementId: Map<string, string>;
-}): number {
-	const minimumAnchorStartTime = Math.max(
-		0,
-		...group.members.map((member) => -member.timeOffset),
-	);
-	let clampedAnchorStartTime = Math.max(
-		minimumAnchorStartTime,
-		anchorStartTime,
+}): MediaTime {
+	const minimumAnchorStartTime = group.members.reduce(
+		(minimumStartTime, member) =>
+			member.timeOffset < ZERO_MEDIA_TIME
+				? maxMediaTime({
+						a: minimumStartTime,
+						b: subMediaTime({
+							a: ZERO_MEDIA_TIME,
+							b: member.timeOffset,
+						}),
+					})
+				: minimumStartTime,
+		ZERO_MEDIA_TIME,
 	);
+	let clampedAnchorStartTime =
+		anchorStartTime < minimumAnchorStartTime
+			? minimumAnchorStartTime
+			: anchorStartTime;
 
 	const memberOnMainTrack = group.members.find(
 		(member) =>
@@ -358,11 +380,13 @@ function clampAnchorStartTime({
 	const movingElementIds = new Set(
 		group.members.map((member) => member.elementId),
 	);
-	const requestedMainStartTime =
-		clampedAnchorStartTime + memberOnMainTrack.timeOffset;
+	const requestedMainStartTime = addMediaTime({
+		a: clampedAnchorStartTime,
+		b: memberOnMainTrack.timeOffset,
+	});
 	const earliestStationaryMainStartTime = tracks.main.elements
 		.filter((element) => !movingElementIds.has(element.id))
-		.reduce<number | null>((earliestStartTime, element) => {
+		.reduce<MediaTime | null>((earliestStartTime, element) => {
 			if (earliestStartTime == null || element.startTime < earliestStartTime) {
 				return element.startTime;
 			}
@@ -373,10 +397,13 @@ function clampAnchorStartTime({
 		earliestStationaryMainStartTime == null ||
 		requestedMainStartTime <= earliestStationaryMainStartTime
 	) {
-		clampedAnchorStartTime = Math.max(
-			minimumAnchorStartTime,
-			-memberOnMainTrack.timeOffset,
-		);
+		clampedAnchorStartTime = maxMediaTime({
+			a: minimumAnchorStartTime,
+			b: subMediaTime({
+				a: ZERO_MEDIA_TIME,
+				b: memberOnMainTrack.timeOffset,
+			}),
+		});
 	}
 
 	return clampedAnchorStartTime;
@@ -422,7 +449,7 @@ function canApplyMovesToExistingTracks({
 			const sourceElement = sourceElements.get(move.elementId);
 			return {
 				startTime: move.newStartTime,
-				duration: sourceElement?.duration ?? 0,
+				duration: sourceElement?.duration ?? ZERO_MEDIA_TIME,
 			};
 		});
 		if (hasOverlappingTimeSpans({ timeSpans })) {
diff --git a/apps/web/src/timeline/group-move/snap.ts b/apps/web/src/timeline/group-move/snap.ts
index 32c0a2f1..aa06a35b 100644
--- a/apps/web/src/timeline/group-move/snap.ts
+++ b/apps/web/src/timeline/group-move/snap.ts
@@ -9,6 +9,7 @@ import { getElementEdgeSnapPoints } from "@/timeline/element-snap-source";
 import { getPlayheadSnapPoints } from "@/timeline/playhead-snap-source";
 import { getAnimationKeyframeSnapPointsForTimeline } from "@/animation/timeline-snap-points";
 import type { MoveGroup } from "./types";
+import { addMediaTime, type MediaTime, subMediaTime } from "@/wasm";
 
 export function snapGroupEdges({
 	group,
@@ -18,12 +19,12 @@ export function snapGroupEdges({
 	zoomLevel,
 }: {
 	group: MoveGroup;
-	anchorStartTime: number;
+	anchorStartTime: MediaTime;
 	tracks: SceneTracks;
-	playheadTime: number;
+	playheadTime: MediaTime;
 	zoomLevel: number;
 }): {
-	snappedAnchorStartTime: number;
+	snappedAnchorStartTime: MediaTime;
 	snapPoint: SnapPoint | null;
 } {
 	const excludeElementIds = new Set(
@@ -47,7 +48,10 @@ export function snapGroupEdges({
 	let snapPoint: SnapPoint | null = null;
 
 	for (const member of group.members) {
-		const memberStartTime = anchorStartTime + member.timeOffset;
+		const memberStartTime = addMediaTime({
+			a: anchorStartTime,
+			b: member.timeOffset,
+		});
 		const memberStartSnap = resolveTimelineSnap({
 			targetTime: memberStartTime,
 			snapPoints,
@@ -58,12 +62,18 @@ export function snapGroupEdges({
 			memberStartSnap.snapDistance < closestSnapDistance
 		) {
 			closestSnapDistance = memberStartSnap.snapDistance;
-			snappedAnchorStartTime = memberStartSnap.snappedTime - member.timeOffset;
+			snappedAnchorStartTime = subMediaTime({
+				a: memberStartSnap.snappedTime as MediaTime,
+				b: member.timeOffset,
+			});
 			snapPoint = memberStartSnap.snapPoint;
 		}
 
 		const memberEndSnap = resolveTimelineSnap({
-			targetTime: memberStartTime + member.duration,
+			targetTime: addMediaTime({
+				a: memberStartTime,
+				b: member.duration,
+			}),
 			snapPoints,
 			maxSnapDistance,
 		});
@@ -72,8 +82,13 @@ export function snapGroupEdges({
 			memberEndSnap.snapDistance < closestSnapDistance
 		) {
 			closestSnapDistance = memberEndSnap.snapDistance;
-			snappedAnchorStartTime =
-				memberEndSnap.snappedTime - member.duration - member.timeOffset;
+			snappedAnchorStartTime = subMediaTime({
+				a: subMediaTime({
+					a: memberEndSnap.snappedTime as MediaTime,
+					b: member.duration,
+				}),
+				b: member.timeOffset,
+			});
 			snapPoint = memberEndSnap.snapPoint;
 		}
 	}
diff --git a/apps/web/src/timeline/group-move/types.ts b/apps/web/src/timeline/group-move/types.ts
index daf9c6e9..f97b698c 100644
--- a/apps/web/src/timeline/group-move/types.ts
+++ b/apps/web/src/timeline/group-move/types.ts
@@ -1,11 +1,12 @@
 import type { ElementRef, ElementType, TrackType } from "@/timeline";
+import type { MediaTime } from "@/wasm";
 
 export type GroupTrackSection = "overlay" | "main" | "audio";
 
 export interface GroupMember extends ElementRef {
 	elementType: ElementType;
-	duration: number;
-	timeOffset: number;
+	duration: MediaTime;
+	timeOffset: MediaTime;
 	trackSection: GroupTrackSection;
 	sectionIndex: number;
 	displayIndex: number;
@@ -26,7 +27,7 @@ export interface PlannedElementMove {
 	sourceTrackId: string;
 	targetTrackId: string;
 	elementId: string;
-	newStartTime: number;
+	newStartTime: MediaTime;
 }
 
 export interface GroupMoveResult {
diff --git a/apps/web/src/timeline/group-resize/compute-resize.ts b/apps/web/src/timeline/group-resize/compute-resize.ts
index dd542967..bbe829cc 100644
--- a/apps/web/src/timeline/group-resize/compute-resize.ts
+++ b/apps/web/src/timeline/group-resize/compute-resize.ts
@@ -3,7 +3,7 @@ import {
 	getSourceSpanAtClipTime,
 	getTimelineDurationForSourceSpan,
 } from "@/retime";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { TICKS_PER_SECOND, roundMediaTime } from "@/wasm";
 import type {
 	ComputeGroupResizeArgs,
 	GroupResizeMember,
@@ -188,15 +188,17 @@ function getSourceDeltaForClipDelta({
 		return clipDelta;
 	}
 
-	return clipDelta >= 0
-		? getSourceSpanAtClipTime({
-				clipTime: clipDelta,
-				retime: member.retime,
-			})
-		: -getSourceSpanAtClipTime({
-				clipTime: Math.abs(clipDelta),
-				retime: member.retime,
-			});
+	const sourceDelta =
+		clipDelta >= 0
+			? getSourceSpanAtClipTime({
+					clipTime: clipDelta,
+					retime: member.retime,
+				})
+			: -getSourceSpanAtClipTime({
+					clipTime: Math.abs(clipDelta),
+					retime: member.retime,
+				});
+	return roundMediaTime({ time: sourceDelta });
 }
 
 function getVisibleSourceSpanForDuration({
@@ -227,9 +229,11 @@ function getDurationForVisibleSourceSpan({
 		return sourceSpan;
 	}
 
-	return getTimelineDurationForSourceSpan({
-		sourceSpan,
-		retime: member.retime,
+	return roundMediaTime({
+		time: getTimelineDurationForSourceSpan({
+			sourceSpan,
+			retime: member.retime,
+		}),
 	});
 }
 
diff --git a/apps/web/src/timeline/hooks/element/use-element-interaction.ts b/apps/web/src/timeline/hooks/element/use-element-interaction.ts
index 621259b9..9caca28a 100644
--- a/apps/web/src/timeline/hooks/element/use-element-interaction.ts
+++ b/apps/web/src/timeline/hooks/element/use-element-interaction.ts
@@ -17,7 +17,14 @@ import {
 	type MoveGroup,
 } from "@/timeline/group-move";
 import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/timeline/scale";
-import { TICKS_PER_SECOND } from "@/wasm";
+import {
+	addMediaTime,
+	type MediaTime,
+	mediaTime,
+	subMediaTime,
+	TICKS_PER_SECOND,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 import { TIMELINE_DRAG_THRESHOLD_PX } from "@/timeline/components/interaction";
 import { roundToFrame } from "opencut-wasm";
 import { computeDropTarget } from "@/timeline/components/drop-target";
@@ -54,9 +61,9 @@ const initialDragState: ElementDragState = {
 	trackId: null,
 	startMouseX: 0,
 	startMouseY: 0,
-	startElementTime: 0,
-	clickOffsetTime: 0,
-	currentTime: 0,
+	startElementTime: ZERO_MEDIA_TIME,
+	clickOffsetTime: ZERO_MEDIA_TIME,
+	currentTime: ZERO_MEDIA_TIME,
 	currentMouseY: 0,
 };
 
@@ -66,8 +73,8 @@ interface PendingDragState {
 	selectedElements: ElementRef[];
 	startMouseX: number;
 	startMouseY: number;
-	startElementTime: number;
-	clickOffsetTime: number;
+	startElementTime: MediaTime;
+	clickOffsetTime: MediaTime;
 }
 
 function getClickOffsetTime({
@@ -78,10 +85,12 @@ function getClickOffsetTime({
 	clientX: number;
 	elementRect: DOMRect;
 	zoomLevel: number;
-}): number {
+}): MediaTime {
 	const clickOffsetX = clientX - elementRect.left;
 	const seconds = clickOffsetX / (BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel);
-	return Math.round(seconds * TICKS_PER_SECOND);
+	return mediaTime({
+		ticks: Math.round(seconds * TICKS_PER_SECOND),
+	});
 }
 
 function getVerticalDragDirection({
@@ -118,7 +127,7 @@ function getDragDropTarget({
 	tracksScrollRef: RefObject<HTMLDivElement | null>;
 	headerRef?: RefObject<HTMLElement | null>;
 	zoomLevel: number;
-	snappedTime: number;
+	snappedTime: MediaTime;
 	verticalDragDirection?: "up" | "down" | null;
 }): DropTarget | null {
 	const containerRect = tracksContainerRef.current?.getBoundingClientRect();
@@ -162,7 +171,7 @@ interface StartDragParams
 		ElementDragState,
 		"isDragging" | "currentTime" | "currentMouseY"
 	> {
-	initialCurrentTime: number;
+	initialCurrentTime: MediaTime;
 	initialCurrentMouseY: number;
 }
 
@@ -249,7 +258,7 @@ export function useElementInteraction({
 			dropTarget,
 		}: {
 			group: MoveGroup;
-			snappedTime: number;
+			snappedTime: MediaTime;
 			dropTarget: DropTarget | null;
 		}): GroupMoveResult | null => {
 			if (!dropTarget) {
@@ -317,7 +326,7 @@ export function useElementInteraction({
 			frameSnappedTime,
 			group,
 		}: {
-			frameSnappedTime: number;
+			frameSnappedTime: MediaTime;
 			group: MoveGroup | null;
 		}) => {
 			if (!group || !snappingEnabled || isShiftHeldRef.current) {
@@ -366,15 +375,19 @@ export function useElementInteraction({
 						zoomLevel,
 						scrollLeft,
 					});
-					const adjustedTime = Math.max(
-						0,
-						mouseTime - pendingDragRef.current.clickOffsetTime,
-					);
-					const snappedTime =
+					const adjustedTime =
+						mouseTime > pendingDragRef.current.clickOffsetTime
+							? subMediaTime({
+									a: mouseTime,
+									b: pendingDragRef.current.clickOffsetTime,
+								})
+							: ZERO_MEDIA_TIME;
+					const snappedTime = (
 						roundToFrame({
 							time: adjustedTime,
 							rate: activeProject.settings.fps,
-						}) ?? adjustedTime;
+						}) ?? adjustedTime
+					) as MediaTime;
 					const moveGroup = buildMoveGroup({
 						anchorRef: {
 							trackId: pendingDragRef.current.trackId,
@@ -389,7 +402,7 @@ export function useElementInteraction({
 
 					moveGroupRef.current = moveGroup;
 					newTrackIdsRef.current = moveGroup.members.map(() => generateUUID());
-					const dragTimeOffsets: Record<string, number> = {};
+					const dragTimeOffsets: Record<string, MediaTime> = {};
 					for (const member of moveGroup.members) {
 						dragTimeOffsets[member.elementId] = member.timeOffset;
 					}
@@ -478,10 +491,17 @@ export function useElementInteraction({
 				zoomLevel,
 				scrollLeft,
 			});
-			const adjustedTime = Math.max(0, mouseTime - dragState.clickOffsetTime);
+			const adjustedTime =
+				mouseTime > dragState.clickOffsetTime
+					? subMediaTime({
+							a: mouseTime,
+							b: dragState.clickOffsetTime,
+						})
+					: ZERO_MEDIA_TIME;
 			const fps = activeProject.settings.fps;
-			const frameSnappedTime =
-				roundToFrame({ time: adjustedTime, rate: fps }) ?? adjustedTime;
+			const frameSnappedTime = (
+				roundToFrame({ time: adjustedTime, rate: fps }) ?? adjustedTime
+			) as MediaTime;
 
 			const moveGroup = moveGroupRef.current;
 			const { snappedTime, snapPoint } = getDragSnapResult({
@@ -596,8 +616,10 @@ export function useElementInteraction({
 				const currentMember = moveGroup.members.find(
 					(member) => member.elementId === move.elementId,
 				);
-				const originalStartTime =
-					dragState.startElementTime + (currentMember?.timeOffset ?? 0);
+				const originalStartTime = addMediaTime({
+					a: dragState.startElementTime,
+					b: currentMember?.timeOffset ?? ZERO_MEDIA_TIME,
+				});
 				return (
 					currentMember?.trackId !== move.targetTrackId ||
 					originalStartTime !== move.newStartTime
diff --git a/apps/web/src/timeline/hooks/element/use-keyframe-drag.ts b/apps/web/src/timeline/hooks/element/use-keyframe-drag.ts
index 92b6f0d8..afead4e9 100644
--- a/apps/web/src/timeline/hooks/element/use-keyframe-drag.ts
+++ b/apps/web/src/timeline/hooks/element/use-keyframe-drag.ts
@@ -11,7 +11,15 @@ import { useKeyframeSelection } from "./use-keyframe-selection";
 import { roundToFrame, snappedSeekTime } from "opencut-wasm";
 import { timelineTimeToSnappedPixels } from "@/timeline";
 import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/timeline/scale";
-import { TICKS_PER_SECOND } from "@/wasm";
+import {
+	addMediaTime,
+	type MediaTime,
+	maxMediaTime,
+	mediaTime,
+	minMediaTime,
+	TICKS_PER_SECOND,
+	ZERO_MEDIA_TIME,
+} from "@/wasm";
 import { TIMELINE_DRAG_THRESHOLD_PX } from "@/timeline/components/interaction";
 import { RetimeKeyframeCommand } from "@/commands/timeline/element/keyframes/retime-keyframe";
 import { BatchCommand } from "@/commands";
@@ -22,13 +30,13 @@ import { registerCanceller } from "@/editor/cancel-interaction";
 export interface KeyframeDragState {
 	isDragging: boolean;
 	draggingKeyframeIds: Set<string>;
-	deltaTime: number;
+	deltaTime: MediaTime;
 }
 
 const initialDragState: KeyframeDragState = {
 	isDragging: false,
 	draggingKeyframeIds: new Set(),
-	deltaTime: 0,
+	deltaTime: ZERO_MEDIA_TIME,
 };
 
 interface PendingKeyframeDrag {
@@ -43,7 +51,7 @@ export function useKeyframeDrag({
 }: {
 	zoomLevel: number;
 	element: TimelineElement;
-	displayedStartTime: number;
+	displayedStartTime: MediaTime;
 }) {
 	const editor = useEditor();
 	const {
@@ -83,7 +91,7 @@ export function useKeyframeDrag({
 			deltaTime,
 		}: {
 			keyframeRefs: SelectedKeyframeRef[];
-			deltaTime: number;
+			deltaTime: MediaTime;
 		}) => {
 			const commands: Command[] = keyframeRefs.flatMap((keyframeRef) => {
 				const keyframe = getKeyframeById({
@@ -92,10 +100,13 @@ export function useKeyframeDrag({
 					keyframeId: keyframeRef.keyframeId,
 				});
 				if (!keyframe) return [];
-				const nextTime = Math.max(
-					0,
-					Math.min(element.duration, keyframe.time + deltaTime),
-				);
+				const nextTime = maxMediaTime({
+					a: ZERO_MEDIA_TIME,
+					b: minMediaTime({
+						a: element.duration,
+						b: addMediaTime({ a: keyframe.time, b: deltaTime }),
+					}),
+				});
 				return [
 					new RetimeKeyframeCommand({
 						trackId: keyframeRef.trackId,
@@ -138,7 +149,7 @@ export function useKeyframeDrag({
 					draggingKeyframeIds: new Set(
 						pending.keyframeRefs.map((keyframe) => keyframe.keyframeId),
 					),
-					deltaTime: 0,
+					deltaTime: ZERO_MEDIA_TIME,
 				});
 				return;
 			}
@@ -146,11 +157,14 @@ export function useKeyframeDrag({
 			if (!dragState.isDragging) return;
 
 			const startX = mouseDownXRef.current ?? clientX;
-			const rawDelta = Math.round(
-				((clientX - startX) / pixelsPerSecond) * TICKS_PER_SECOND,
-			);
-			const snappedDelta =
-				roundToFrame({ time: rawDelta, rate: fps }) ?? rawDelta;
+			const rawDelta = mediaTime({
+				ticks: Math.round(
+					((clientX - startX) / pixelsPerSecond) * TICKS_PER_SECOND,
+				),
+			});
+			const snappedDelta = (
+				roundToFrame({ time: rawDelta, rate: fps }) ?? rawDelta
+			) as MediaTime;
 
 			setDragState((previous) => ({ ...previous, deltaTime: snappedDelta }));
 		};
@@ -246,7 +260,7 @@ export function useKeyframeDrag({
 			event: ReactMouseEvent;
 			keyframes: SelectedKeyframeRef[];
 			orderedKeyframes: SelectedKeyframeRef[];
-			indicatorTime: number;
+			indicatorTime: MediaTime;
 		}) => {
 			event.stopPropagation();
 
@@ -259,12 +273,17 @@ export function useKeyframeDrag({
 			if (wasDrag) return;
 
 			const duration = editor.timeline.getTotalDuration();
-			const seekTime =
+			const absoluteIndicatorTime = addMediaTime({
+				a: displayedStartTime,
+				b: indicatorTime,
+			});
+			const seekTime = (
 				snappedSeekTime({
-					time: displayedStartTime + indicatorTime,
+					time: absoluteIndicatorTime,
 					duration,
 					rate: fps,
-				}) ?? displayedStartTime + indicatorTime;
+				}) ?? absoluteIndicatorTime
+			) as MediaTime;
 			editor.playback.seek({ time: seekTime });
 
 			if (event.shiftKey) {
diff --git a/apps/web/src/timeline/hooks/use-timeline-drag-drop.ts b/apps/web/src/timeline/hooks/use-timeline-drag-drop.ts
index 775b7337..5a892ccf 100644
--- a/apps/web/src/timeline/hooks/use-timeline-drag-drop.ts
+++ b/apps/web/src/timeline/hooks/use-timeline-drag-drop.ts
@@ -4,7 +4,7 @@ import { processMediaAssets } from "@/media/processing";
 import { toast } from "sonner";
 import { showMediaUploadToast } from "@/media/upload-toast";
 import { DEFAULT_NEW_ELEMENT_DURATION } from "@/timeline/creation";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTimeFromSeconds, type MediaTime } from "@/wasm";
 import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/timeline/scale";
 import { roundToFrame } from "opencut-wasm";
 import {
@@ -45,9 +45,9 @@ export function useTimelineDragDrop({
 	const [dragElementType, setElementType] = useState<ElementType | null>(null);
 
 	const getSnappedTime = useCallback(
-		({ time }: { time: number }) => {
+		({ time }: { time: MediaTime }) => {
 			const projectFps = editor.project.getActive().settings.fps;
-			return roundToFrame({ time, rate: projectFps }) ?? time;
+			return (roundToFrame({ time, rate: projectFps }) ?? time) as MediaTime;
 		},
 		[editor],
 	);
@@ -76,7 +76,7 @@ export function useTimelineDragDrop({
 		}: {
 			elementType: ElementType;
 			mediaId?: string;
-		}): number => {
+		}): MediaTime => {
 			if (
 				elementType === "text" ||
 				elementType === "graphic" ||
@@ -89,7 +89,7 @@ export function useTimelineDragDrop({
 				const mediaAssets = editor.media.getAssets();
 				const media = mediaAssets.find((m) => m.id === mediaId);
 				return media?.duration != null
-					? Math.round(media.duration * TICKS_PER_SECOND)
+					? mediaTimeFromSeconds({ seconds: media.duration })
 					: DEFAULT_NEW_ELEMENT_DURATION;
 			}
 			return DEFAULT_NEW_ELEMENT_DURATION;
@@ -346,7 +346,7 @@ export function useTimelineDragDrop({
 
 			const duration =
 				mediaAsset.duration != null
-					? Math.round(mediaAsset.duration * TICKS_PER_SECOND)
+					? mediaTimeFromSeconds({ seconds: mediaAsset.duration })
 					: DEFAULT_NEW_ELEMENT_DURATION;
 			const element = buildElementFromMedia({
 				mediaId: mediaAsset.id,
@@ -470,7 +470,7 @@ export function useTimelineDragDrop({
 
 						const duration =
 							createdAsset.duration != null
-								? Math.round(createdAsset.duration * TICKS_PER_SECOND)
+								? mediaTimeFromSeconds({ seconds: createdAsset.duration })
 								: DEFAULT_NEW_ELEMENT_DURATION;
 						const sceneTracks = editor.scenes.getActiveScene().tracks;
 						const currentTime = editor.playback.getCurrentTime();
diff --git a/apps/web/src/timeline/hooks/use-timeline-playhead.ts b/apps/web/src/timeline/hooks/use-timeline-playhead.ts
index 7d9cf447..6fbf2147 100644
--- a/apps/web/src/timeline/hooks/use-timeline-playhead.ts
+++ b/apps/web/src/timeline/hooks/use-timeline-playhead.ts
@@ -1,5 +1,5 @@
 import { snappedSeekTime } from "opencut-wasm";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTime, type MediaTime, TICKS_PER_SECOND } from "@/wasm";
 import { useEffect, useCallback, useRef } from "react";
 import { useEdgeAutoScroll } from "@/timeline/hooks/use-edge-auto-scroll";
 import { useEditor } from "@/editor/use-editor";
@@ -53,11 +53,11 @@ export function useTimelinePlayhead({
 	}, [zoomLevel, duration, isScrubbing, editor.playback]);
 
 	const seek = useCallback(
-		({ time }: { time: number }) => editor.playback.seek({ time }),
+		({ time }: { time: MediaTime }) => editor.playback.seek({ time }),
 		[editor.playback],
 	);
 
-	const scrubTimeRef = useRef<number | null>(null);
+	const scrubTimeRef = useRef<MediaTime | null>(null);
 	const isDraggingRulerRef = useRef(false);
 	const hasDraggedRulerRef = useRef(false);
 	const lastMouseXRef = useRef<number>(0);
@@ -92,11 +92,14 @@ export function useTimelinePlayhead({
 					clampedMouseX / (BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel),
 				),
 			);
-			const rawTime = Math.round(rawTimeSeconds * TICKS_PER_SECOND);
+			const rawTime = mediaTime({
+				ticks: Math.round(rawTimeSeconds * TICKS_PER_SECOND),
+			});
 
 			const rate = activeProject.settings.fps;
-			const frameTime =
-				snappedSeekTime({ time: rawTime, duration, rate }) ?? rawTime;
+			const frameTime = (
+				snappedSeekTime({ time: rawTime, duration, rate }) ?? rawTime
+			) as MediaTime;
 
 			const shouldSnap = snappingEnabled && !isShiftHeldRef.current;
 			const time = (() => {
@@ -224,7 +227,7 @@ export function useTimelinePlayhead({
 	}, [isScrubbing, seek, handleScrub, editor, tracksScrollRef, zoomLevel]);
 
 	const updatePlayheadLeft = useCallback(
-		(time: number) => {
+		(time: MediaTime) => {
 			const playheadEl = playheadRef?.current;
 			if (!playheadEl) return;
 			const centerPosition = timelineTimeToSnappedPixels({
@@ -251,8 +254,7 @@ export function useTimelinePlayhead({
 	}, [editor.playback, rulerScrollRef, updatePlayheadLeft]);
 
 	useEffect(() => {
-		const handlePlaybackUpdate = (e: Event) => {
-			const time = (e as CustomEvent<{ time: number }>).detail.time;
+		const handlePlaybackTime = (time: MediaTime) => {
 			updatePlayheadLeft(time);
 
 			if (!isPlayingRef.current || isScrubbingRef.current) return;
@@ -280,11 +282,12 @@ export function useTimelinePlayhead({
 				rulerViewport.scrollLeft = tracksViewport.scrollLeft = desiredScroll;
 			}
 		};
+		const handlePlaybackUpdate = (e: Event) => {
+			handlePlaybackTime((e as CustomEvent<{ time: MediaTime }>).detail.time);
+		};
 
 		const initialTime = editor.playback.getCurrentTime();
-		handlePlaybackUpdate({
-			detail: { time: initialTime },
-		} as CustomEvent<{ time: number }>);
+		handlePlaybackTime(initialTime);
 
 		window.addEventListener("playback-update", handlePlaybackUpdate);
 		window.addEventListener("playback-seek", handlePlaybackUpdate);
diff --git a/apps/web/src/timeline/hooks/use-timeline-resize.ts b/apps/web/src/timeline/hooks/use-timeline-resize.ts
index fb8da291..accda4a1 100644
--- a/apps/web/src/timeline/hooks/use-timeline-resize.ts
+++ b/apps/web/src/timeline/hooks/use-timeline-resize.ts
@@ -139,7 +139,7 @@ export function useTimelineResize({
 				updates: result.updates.map(({ trackId, elementId, patch }) => ({
 					trackId,
 					elementId,
-					updates: patch,
+					updates: patch as Partial<TimelineElement>,
 				})),
 			});
 		};
@@ -155,7 +155,7 @@ export function useTimelineResize({
 					updates: result.updates.map(({ trackId, elementId, patch }) => ({
 						trackId,
 						elementId,
-						patch,
+						patch: patch as Partial<TimelineElement>,
 					})),
 				});
 			}
diff --git a/apps/web/src/timeline/hooks/use-timeline-seek.ts b/apps/web/src/timeline/hooks/use-timeline-seek.ts
index 889177c9..88a8268d 100644
--- a/apps/web/src/timeline/hooks/use-timeline-seek.ts
+++ b/apps/web/src/timeline/hooks/use-timeline-seek.ts
@@ -2,7 +2,7 @@ import { useCallback, useRef } from "react";
 import type { MutableRefObject, RefObject } from "react";
 import { BASE_TIMELINE_PIXELS_PER_SECOND } from "@/timeline/scale";
 import { snappedSeekTime } from "opencut-wasm";
-import { TICKS_PER_SECOND } from "@/wasm";
+import { mediaTime, type MediaTime, TICKS_PER_SECOND } from "@/wasm";
 import { useEditor } from "@/editor/use-editor";
 
 interface UseTimelineSeekProps {
@@ -11,10 +11,10 @@ interface UseTimelineSeekProps {
 	rulerScrollRef: RefObject<HTMLDivElement | null>;
 	tracksScrollRef: RefObject<HTMLDivElement | null>;
 	zoomLevel: number;
-	duration: number;
+	duration: MediaTime;
 	isSelecting: boolean;
 	clearSelectedElements: () => void;
-	seek: (time: number) => void;
+	seek: (time: MediaTime) => void;
 }
 
 function resetMouseTracking({
@@ -135,11 +135,13 @@ export function useTimelineSeek({
 					(mouseX + scrollLeft) / (BASE_TIMELINE_PIXELS_PER_SECOND * zoomLevel),
 				),
 			);
-			const rawTime = Math.round(rawTimeSeconds * TICKS_PER_SECOND);
+			const rawTime = mediaTime({
+				ticks: Math.round(rawTimeSeconds * TICKS_PER_SECOND),
+			});
 
 			const rate = activeProject?.settings.fps;
 			const time = rate
-				? (snappedSeekTime({ time: rawTime, duration, rate }) ?? rawTime)
+				? ((snappedSeekTime({ time: rawTime, duration, rate }) ?? rawTime) as MediaTime)
 				: rawTime;
 			seek(time);
 			editor.project.setTimelineViewState({
diff --git a/apps/web/src/timeline/hooks/use-timeline-zoom.ts b/apps/web/src/timeline/hooks/use-timeline-zoom.ts
index 7929d495..0f75face 100644
--- a/apps/web/src/timeline/hooks/use-timeline-zoom.ts
+++ b/apps/web/src/timeline/hooks/use-timeline-zoom.ts
@@ -12,13 +12,14 @@ import { TIMELINE_ZOOM_MAX, TIMELINE_ZOOM_MIN } from "@/timeline/scale";
 import { timelineTimeToPixels } from "@/timeline/pixel-utils";
 import { useEditor } from "@/editor/use-editor";
 import { zoomToSlider } from "@/timeline/zoom-utils";
+import type { MediaTime } from "@/wasm";
 
 interface UseTimelineZoomProps {
 	containerRef: RefObject<HTMLDivElement | null>;
 	minZoom?: number;
 	initialZoom?: number;
 	initialScrollLeft?: number;
-	initialPlayheadTime?: number;
+	initialPlayheadTime?: MediaTime;
 	tracksScrollRef: RefObject<HTMLDivElement | null>;
 	rulerScrollRef: RefObject<HTMLDivElement | null>;
 }
@@ -106,7 +107,7 @@ export function useTimelineZoom({
 			setZoomLevel(Math.max(minZoom, Math.min(TIMELINE_ZOOM_MAX, initialZoom)));
 			return;
 		}
-		setZoomLevel((prev) => {
+		setZoomLevel((prev: number) => {
 			if (prev < minZoom) {
 				return minZoom;
 			}
@@ -116,7 +117,7 @@ export function useTimelineZoom({
 
 	const wrappedSetZoomLevel = useCallback(
 		(zoomLevelOrUpdater: number | ((prev: number) => number)) => {
-			setZoomLevel((prev) => {
+			setZoomLevel((prev: number) => {
 				const nextZoom =
 					typeof zoomLevelOrUpdater === "function"
 						? zoomLevelOrUpdater(prev)
diff --git a/apps/web/src/timeline/index.ts b/apps/web/src/timeline/index.ts
index 5ee079b1..3775e006 100644
--- a/apps/web/src/timeline/index.ts
+++ b/apps/web/src/timeline/index.ts
@@ -1,29 +1,32 @@
-import type { SceneTracks } from "./types";

-

-export * from "./types";

-export * from "./drag";

-export * from "./track-capabilities";

-export * from "./track-element-update";

-export * from "./element-utils";

-export * from "./audio-separation";

-export * from "./zoom-utils";

-export * from "./ruler-utils";

-export * from "./pixel-utils";

-

-export function calculateTotalDuration({

-	tracks,

-}: {

-	tracks: SceneTracks;

-}): number {

-	const orderedTracks = [...tracks.overlay, tracks.main, ...tracks.audio];

-	if (orderedTracks.length === 0) return 0;

-

-	const trackEndTimes = orderedTracks.map((track) =>

-		track.elements.reduce((maxEnd, element) => {

-			const elementEnd = element.startTime + element.duration;

-			return Math.max(maxEnd, elementEnd);

-		}, 0),

-	);

-

-	return Math.max(...trackEndTimes, 0);

-}

+import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
+import type { SceneTracks } from "./types";
+
+export * from "./types";
+export * from "./drag";
+export * from "./track-capabilities";
+export * from "./track-element-update";
+export * from "./element-utils";
+export * from "./audio-separation";
+export * from "./zoom-utils";
+export * from "./ruler-utils";
+export * from "./pixel-utils";
+
+export function calculateTotalDuration({
+	tracks,
+}: {
+	tracks: SceneTracks;
+}): MediaTime {
+	const orderedTracks = [...tracks.overlay, tracks.main, ...tracks.audio];
+	if (orderedTracks.length === 0) return ZERO_MEDIA_TIME;
+
+	let maxEnd: MediaTime = ZERO_MEDIA_TIME;
+	for (const track of orderedTracks) {
+		for (const element of track.elements) {
+			// `startTime + duration` is integer-by-construction (both `MediaTime`),
+			// so the cast re-establishes the brand without runtime work.
+			const elementEnd = (element.startTime + element.duration) as MediaTime;
+			if (elementEnd > maxEnd) maxEnd = elementEnd;
+		}
+	}
+	return maxEnd;
+}
diff --git a/apps/web/src/timeline/placement/__tests__/resolve.test.ts b/apps/web/src/timeline/placement/__tests__/resolve.test.ts
index ebbfe578..44f0a1fe 100644
--- a/apps/web/src/timeline/placement/__tests__/resolve.test.ts
+++ b/apps/web/src/timeline/placement/__tests__/resolve.test.ts
@@ -14,6 +14,7 @@ import type {
 } from "@/timeline";
 import type { Transform } from "@/rendering";
 import { resolveTrackPlacement } from "@/timeline/placement";
+import { mediaTime, ZERO_MEDIA_TIME } from "@/wasm";
 
 function buildTransform(): Transform {
 	return {
@@ -67,10 +68,10 @@ function buildElement({
 				id,
 				type: "audio",
 				name: id,
-				startTime,
-				duration,
-				trimStart: 0,
-				trimEnd: 0,
+				startTime: mediaTime({ ticks: startTime }),
+				duration: mediaTime({ ticks: duration }),
+				trimStart: ZERO_MEDIA_TIME,
+				trimEnd: ZERO_MEDIA_TIME,
 				volume: 1,
 				sourceType: "upload",
 				mediaId: `media-${id}`,
@@ -80,10 +81,10 @@ function buildElement({
 				id,
 				type: "graphic",
 				name: id,
-				startTime,
-				duration,
-				trimStart: 0,
-				trimEnd: 0,
+				startTime: mediaTime({ ticks: startTime }),
+				duration: mediaTime({ ticks: duration }),
+				trimStart: ZERO_MEDIA_TIME,
+				trimEnd: ZERO_MEDIA_TIME,
 				definitionId: `graphic-${id}`,
 				params: {},
 				transform: buildTransform(),
@@ -94,10 +95,10 @@ function buildElement({
 				id,
 				type: "text",
 				name: id,
-				startTime,
-				duration,
-				trimStart: 0,
-				trimEnd: 0,
+				startTime: mediaTime({ ticks: startTime }),
+				duration: mediaTime({ ticks: duration }),
+				trimStart: ZERO_MEDIA_TIME,
+				trimEnd: ZERO_MEDIA_TIME,
 				content: id,
 				fontSize: 32,
 				fontFamily: "sans-serif",
@@ -118,10 +119,10 @@ function buildElement({
 				id,
 				type: "video",
 				name: id,
-				startTime,
-				duration,
-				trimStart: 0,
-				trimEnd: 0,
+				startTime: mediaTime({ ticks: startTime }),
+				duration: mediaTime({ ticks: duration }),
+				trimStart: ZERO_MEDIA_TIME,
+				trimEnd: ZERO_MEDIA_TIME,
 				mediaId: `media-${id}`,
 				transform: buildTransform(),
 				opacity: 1,
@@ -224,7 +225,11 @@ function buildTimeSpan({
 	duration: number;
 	excludeElementId?: string;
 }) {
-	return { startTime, duration, excludeElementId };
+	return {
+		startTime: mediaTime({ ticks: startTime }),
+		duration: mediaTime({ ticks: duration }),
+		excludeElementId,
+	};
 }
 
 function buildSceneTracks({
diff --git a/apps/web/src/timeline/placement/main-track.ts b/apps/web/src/timeline/placement/main-track.ts
index ab2ab7bd..36632226 100644
--- a/apps/web/src/timeline/placement/main-track.ts
+++ b/apps/web/src/timeline/placement/main-track.ts
@@ -1,4 +1,5 @@
 import type { SceneTracks, TimelineElement, VideoTrack } from "@/timeline";
+import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";
 
 export const MAIN_TRACK_NAME = "Main Track";
 
@@ -31,9 +32,9 @@ export function enforceMainTrackStart({
 }: {
 	tracks: SceneTracks;
 	targetTrackId: string;
-	requestedStartTime: number;
+	requestedStartTime: MediaTime;
 	excludeElementId?: string;
-}): number {
+}): MediaTime {
 	if (tracks.main.id !== targetTrackId) {
 		return requestedStartTime;
 	}
@@ -43,11 +44,11 @@ export function enforceMainTrackStart({
 		excludeElementId,
 	});
 	if (!earliestElement) {
-		return 0;
+		return ZERO_MEDIA_TIME;
 	}
 
 	if (requestedStartTime <= earliestElement.startTime) {
-		return 0;
+		return ZERO_MEDIA_TIME;
 	}
 
 	return requestedStartTime;
diff --git a/apps/web/src/timeline/placement/resolve.ts b/apps/web/src/timeline/placement/resolve.ts
index 26275392..680cb0bb 100644
--- a/apps/web/src/timeline/placement/resolve.ts
+++ b/apps/web/src/timeline/placement/resolve.ts
@@ -13,6 +13,7 @@ import type {
 	PlacementSubject,
 	PlacementTimeSpan,
 } from "./types";
+import { ZERO_MEDIA_TIME } from "@/wasm";
 
 type ResolveTrackPlacementParams = PlacementSubject & {
 	tracks: SceneTracks;
@@ -32,7 +33,7 @@ function buildExistingTrackResult({
 	timeSpans: PlacementTimeSpan[];
 }): PlacementResult {
 	const firstSpan = timeSpans[0];
-	const requestedStartTime = firstSpan?.startTime ?? 0;
+	const requestedStartTime = firstSpan?.startTime ?? ZERO_MEDIA_TIME;
 	const adjustedStartTime = enforceMainTrackStart({
 		tracks,
 		targetTrackId: track.id,
diff --git a/apps/web/src/timeline/placement/types.ts b/apps/web/src/timeline/placement/types.ts
index 6847ab36..748f34d7 100644
--- a/apps/web/src/timeline/placement/types.ts
+++ b/apps/web/src/timeline/placement/types.ts
@@ -1,8 +1,9 @@
 import type { ElementType, TrackType } from "@/timeline";
+import type { MediaTime } from "@/wasm";
 
 export interface PlacementTimeSpan {
-	startTime: number;
-	duration: number;
+	startTime: MediaTime;
+	duration: MediaTime;
 	excludeElementId?: string;
 }
 
@@ -29,7 +30,7 @@ export type PlacementResult =
 			trackId: string;
 			trackIndex: number;
 			trackType: TrackType;
-			adjustedStartTime?: number;
+			adjustedStartTime?: MediaTime;
 	  }
 	| {
 			kind: "newTrack";
diff --git a/apps/web/src/timeline/scenes.ts b/apps/web/src/timeline/scenes.ts
index d48c943c..8aa1b6b5 100644
--- a/apps/web/src/timeline/scenes.ts
+++ b/apps/web/src/timeline/scenes.ts
@@ -2,6 +2,7 @@ import type { TScene } from "@/timeline";
 import { generateUUID } from "@/utils/id";

 import { calculateTotalDuration } from "@/timeline";

 import { MAIN_TRACK_NAME } from "@/timeline/placement/main-track";

+import { type MediaTime, ZERO_MEDIA_TIME } from "@/wasm";

 

 export function getMainScene({ scenes }: { scenes: TScene[] }): TScene | null {

 	return scenes.find((scene) => scene.isMain) || null;

@@ -89,10 +90,10 @@ export function getProjectDurationFromScenes({
 	scenes,

 }: {

 	scenes: TScene[];

-}): number {

+}): MediaTime {

 	const mainScene = getMainScene({ scenes }) ?? scenes[0] ?? null;

 	if (!mainScene?.tracks) {

-		return 0;

+		return ZERO_MEDIA_TIME;

 	}

 

 	return calculateTotalDuration({ tracks: mainScene.tracks });

diff --git a/apps/web/src/timeline/types.ts b/apps/web/src/timeline/types.ts
index cd543cdf..2a30a065 100644
--- a/apps/web/src/timeline/types.ts
+++ b/apps/web/src/timeline/types.ts
@@ -3,6 +3,7 @@ import type { Effect } from "@/effects/types";
 import type { Mask } from "@/masks/types";

 import type { ParamValues } from "@/params";

 import type { BlendMode, Transform } from "@/rendering";

+import type { MediaTime } from "@/wasm";

 

 export type ElementRef = {

 	trackId: string;

@@ -10,10 +11,10 @@ export type ElementRef = {
 };

 

 export interface Bookmark {

-	time: number;

+	time: MediaTime;

 	note?: string;

 	color?: string;

-	duration?: number;

+	duration?: MediaTime;

 }

 

 export interface TScene {

@@ -107,11 +108,11 @@ export type AudioElement = UploadAudioElement | LibraryAudioElement;
 interface BaseTimelineElement {

 	id: string;

 	name: string;

-	duration: number;

-	startTime: number;

-	trimStart: number;

-	trimEnd: number;

-	sourceDuration?: number;

+	duration: MediaTime;

+	startTime: MediaTime;

+	trimStart: MediaTime;

+	trimEnd: MediaTime;

+	sourceDuration?: MediaTime;

 	animations?: ElementAnimations;

 }

 

@@ -273,13 +274,13 @@ export interface ElementDragState {
 	isDragging: boolean;

 	elementId: string | null;

 	dragElementIds: string[];

-	dragTimeOffsets: Record<string, number>;

+	dragTimeOffsets: Record<string, MediaTime>;

 	trackId: string | null;

 	startMouseX: number;

 	startMouseY: number;

-	startElementTime: number;

-	clickOffsetTime: number;

-	currentTime: number;

+	startElementTime: MediaTime;

+	clickOffsetTime: MediaTime;

+	currentTime: MediaTime;

 	currentMouseY: number;

 }

 

@@ -287,7 +288,7 @@ export interface DropTarget {
 	trackIndex: number;

 	isNewTrack: boolean;

 	insertPosition: "above" | "below" | null;

-	xPosition: number;

+	xPosition: MediaTime;

 	targetElement: { elementId: string; trackId: string } | null;

 }

 

@@ -296,13 +297,13 @@ export interface ComputeDropTargetParams {
 	mouseX: number;

 	mouseY: number;

 	tracks: SceneTracks;

-	playheadTime: number;

+	playheadTime: MediaTime;

 	isExternalDrop: boolean;

-	elementDuration: number;

+	elementDuration: MediaTime;

 	pixelsPerSecond: number;

 	zoomLevel: number;

 	verticalDragDirection?: "up" | "down" | null;

-	startTimeOverride?: number;

+	startTimeOverride?: MediaTime;

 	excludeElementId?: string;

 	targetElementTypes?: string[];

 }

diff --git a/apps/web/src/timeline/update-pipeline.ts b/apps/web/src/timeline/update-pipeline.ts
index beacf897..7ab129e9 100644
--- a/apps/web/src/timeline/update-pipeline.ts
+++ b/apps/web/src/timeline/update-pipeline.ts
@@ -6,6 +6,7 @@ import {
 } from "@/retime";
 import type { RetimeConfig, SceneTracks, TimelineElement } from "@/timeline";
 import { isRetimableElement } from "@/timeline";
+import { ZERO_MEDIA_TIME, roundMediaTime } from "@/wasm";
 
 type ElementUpdateField = keyof TimelineElement | string;
 
@@ -61,9 +62,11 @@ const deriveRules: ElementUpdateRule[] = [
 				0,
 				sourceDuration - element.trimStart - element.trimEnd,
 			);
-			const nextDuration = getTimelineDurationForSourceSpan({
-				sourceSpan: visibleSourceSpan,
-				retime: nextRetime,
+			const nextDuration = roundMediaTime({
+				time: getTimelineDurationForSourceSpan({
+					sourceSpan: visibleSourceSpan,
+					retime: nextRetime,
+				}),
 			});
 
 			return {
@@ -94,7 +97,10 @@ const enforceRules: ElementUpdateRule[] = [
 	{
 		triggers: ["startTime"],
 		apply: ({ element, context }) => {
-			const requestedStartTime = Math.max(0, element.startTime);
+			const requestedStartTime =
+				element.startTime < ZERO_MEDIA_TIME
+					? ZERO_MEDIA_TIME
+					: element.startTime;
 			if (context.trackId !== context.tracks.main.id) {
 				return {
 					element: {
@@ -118,7 +124,7 @@ const enforceRules: ElementUpdateRule[] = [
 					...element,
 					startTime:
 						!earliestElement || requestedStartTime <= earliestElement.startTime
-							? 0
+							? ZERO_MEDIA_TIME
 							: requestedStartTime,
 				},
 			};
diff --git a/apps/web/src/wasm/index.ts b/apps/web/src/wasm/index.ts
index 60031a0e..c979b620 100644
--- a/apps/web/src/wasm/index.ts
+++ b/apps/web/src/wasm/index.ts
@@ -1 +1 @@
-export * from "./ticks";
+export * from "./media-time";
diff --git a/apps/web/src/wasm/media-time.ts b/apps/web/src/wasm/media-time.ts
new file mode 100644
index 00000000..7209e81c
--- /dev/null
+++ b/apps/web/src/wasm/media-time.ts
@@ -0,0 +1,129 @@
+import {
+	TICKS_PER_SECOND as _TICKS_PER_SECOND,
+	mediaTimeFromSeconds as _mediaTimeFromSeconds,
+	mediaTimeToSeconds as _mediaTimeToSeconds,
+} from "opencut-wasm";
+
+/**
+ * Integer-tick time. Mirrors `MediaTime(i64)` in `rust/crates/time/src/media_time.rs`.
+ *
+ * `opencut-wasm` exposes `MediaTime` as a bare `number` alias because tsify
+ * collapses tuple structs. The brand here is the TS-side discipline that
+ * recovers the invariant: a `MediaTime` is an integer count of ticks, and the
+ * only legal way to construct one from a fractional `number` is `roundMediaTime`
+ * (or `mediaTimeFromSeconds`, which rounds inside the wasm boundary).
+ *
+ * Reading is free — `MediaTime` is assignable to `number`. Writing is gated —
+ * a bare `number` is not assignable to `MediaTime`.
+ */
+export type MediaTime = number & { readonly __mediaTime: unique symbol };
+
+export const TICKS_PER_SECOND = _TICKS_PER_SECOND();
+
+export const ZERO_MEDIA_TIME = 0 as MediaTime;
+
+/**
+ * Construct a `MediaTime` from a known-integer tick count. Asserts in dev that
+ * the value is actually an integer; cast in release. Use `roundMediaTime` when
+ * the input may be fractional.
+ */
+export function mediaTime({ ticks }: { ticks: number }): MediaTime {
+	if (process.env.NODE_ENV !== "production" && !Number.isInteger(ticks)) {
+		throw new Error(
+			`mediaTime() requires an integer tick count, got ${ticks}. Use roundMediaTime() for fractional values.`,
+		);
+	}
+	return ticks as MediaTime;
+}
+
+/**
+ * Project a fractional value onto the integer-tick lattice.
+ *
+ * Rounds half away from zero (`-1.5 → -2`, `1.5 → 2`) and normalises `-0` to
+ * `0`. The away-from-zero rule matches Rust's `.round()` and avoids the
+ * `Math.round(-0.5) === -0` quirk that propagates `-0` into stored data.
+ */
+export function roundMediaTime({ time }: { time: number }): MediaTime {
+	const roundedMagnitude = Math.round(Math.abs(time));
+	if (roundedMagnitude === 0) {
+		return 0 as MediaTime;
+	}
+	return (time < 0 ? -roundedMagnitude : roundedMagnitude) as MediaTime;
+}
+
+export function mediaTimeFromSeconds({
+	seconds,
+}: {
+	seconds: number;
+}): MediaTime {
+	const result = _mediaTimeFromSeconds({ seconds });
+	if (result === undefined) {
+		throw new Error(
+			`mediaTimeFromSeconds: rust returned undefined for seconds=${seconds}`,
+		);
+	}
+	return result as MediaTime;
+}
+
+export function mediaTimeToSeconds({ time }: { time: MediaTime }): number {
+	return _mediaTimeToSeconds({ time });
+}
+
+/**
+ * Sum `MediaTime` values. Inputs are integer ticks, so the sum is integer too;
+ * the cast is a no-op at runtime, only re-establishes the brand for the type
+ * system.
+ */
+export function addMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a + b) as MediaTime;
+}
+
+export function subMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a - b) as MediaTime;
+}
+
+export function maxMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a > b ? a : b) as MediaTime;
+}
+
+export function minMediaTime({
+	a,
+	b,
+}: {
+	a: MediaTime;
+	b: MediaTime;
+}): MediaTime {
+	return (a < b ? a : b) as MediaTime;
+}
+
+export function clampMediaTime({
+	time,
+	min,
+	max,
+}: {
+	time: MediaTime;
+	min: MediaTime;
+	max: MediaTime;
+}): MediaTime {
+	if (time < min) return min;
+	if (time > max) return max;
+	return time;
+}
diff --git a/apps/web/src/wasm/ticks.ts b/apps/web/src/wasm/ticks.ts
deleted file mode 100644
index ababe6b3..00000000
--- a/apps/web/src/wasm/ticks.ts
+++ /dev/null
@@ -1,3 +0,0 @@
-import { TICKS_PER_SECOND as _TICKS_PER_SECOND } from "opencut-wasm";
-
-export const TICKS_PER_SECOND = _TICKS_PER_SECOND();