heygen-com · miguel-heygen · Jul 18, 2026
diff --git a/packages/studio/src/player/components/BeatStrip.tsx b/packages/studio/src/player/components/BeatStrip.tsx
@@ -1,7 +1,8 @@
 import { memo, useRef, useState } from "react";
 import { moveBeatCompositionTime, deleteBeatAtCompositionTime } from "../../utils/beatEditActions";
 import { usePlayerStore } from "../store/playerStore";
-import { CLIP_Y } from "./timelineLayout";
+import { CLIP_Y, getTimelineBeatEntries } from "./timelineLayout";
+import type { TimelineTimeRange } from "../lib/timelineClipIndex";
 
 export const BEAT_BAND_H = 14; // dark band height at top of track
 const BEAT_HIT_W = 12; // grab width per beat (px)
@@ -24,23 +25,30 @@ export const BeatBackgroundLines = memo(function BeatBackgroundLines({
   beatStrengths,
   pps,
   highlightTime,
+  renderTimeRange,
 }: {
   beatTimes: number[] | undefined;
   beatStrengths: number[] | undefined;
   pps: number;
   /** Snap guide time — drawn as a bright line even when it is not a beat. */
   highlightTime?: number | null;
+  renderTimeRange?: TimelineTimeRange;
 }) {
   const visibleBeatTimes = beatTimes && !beatsTooDense(beatTimes, pps) ? beatTimes : null;
   const highlightIsBeat =
     highlightTime != null &&
     visibleBeatTimes?.some((t) => Math.abs(t - highlightTime) < 1e-3) === true;
   if (!visibleBeatTimes && highlightTime == null) return null;
+  const beatEntries = getTimelineBeatEntries(
+    visibleBeatTimes ?? undefined,
+    beatStrengths,
+    renderTimeRange,
+  );
   return (
     <div className="absolute inset-0 pointer-events-none" style={{ zIndex: 0 }}>
-      {visibleBeatTimes?.map((t, i) => {
+      {beatEntries.map(({ time: t, index: i, strength: beatStrength }) => {
         const isHighlight = highlightTime != null && Math.abs(t - highlightTime) < 1e-3;
-        const strength = Math.pow(Math.min(1, beatStrengths?.[i] ?? 0.5), 2.2);
+        const strength = Math.pow(Math.min(1, beatStrength ?? 0.5), 2.2);
         const opacity = isHighlight ? 1 : 0.06 + strength * 0.16;
         return (
           <div
@@ -81,26 +89,34 @@ export const BeatStrip = memo(function BeatStrip({
   beatTimes,
   beatStrengths,
   pps,
+  renderTimeRange,
 }: {
   beatTimes: number[] | undefined;
   beatStrengths: number[] | undefined;
   pps: number;
+  renderTimeRange?: TimelineTimeRange;
 }) {
   // Active drag: which beat and how far (px) it's been dragged.
   const [drag, setDrag] = useState<{ index: number; dx: number } | null>(null);
   const dragRef = useRef<{ index: number; startX: number; origTime: number } | null>(null);
 
   if (!beatTimes || beatsTooDense(beatTimes, pps)) return null;
   const cy = BEAT_BAND_H / 2;
+  const beatEntries = getTimelineBeatEntries(
+    beatTimes,
+    beatStrengths,
+    renderTimeRange,
+    drag ? new Set([drag.index]) : undefined,
+  );
 
   return (
     <div
       className="absolute left-0 right-0 pointer-events-none"
       style={{ top: CLIP_Y, height: BEAT_BAND_H, background: "rgba(0,0,0,0.28)", zIndex: 11 }}
     >
-      {beatTimes.map((t, i) => {
+      {beatEntries.map(({ time: t, index: i, strength: beatStrength }) => {
         // Louder beats → larger, brighter dot. Gamma curve widens the contrast.
-        const strength = Math.pow(Math.min(1, beatStrengths?.[i] ?? 0.5), 2.2);
+        const strength = Math.pow(Math.min(1, beatStrength ?? 0.5), 2.2);
         const r = 1.5 + strength * 2.5;
         const opacity = 0.25 + strength * 0.75;
         const dxPx = drag?.index === i ? drag.dx : 0;

diff --git a/packages/studio/src/player/components/TimelineRuler.tsx b/packages/studio/src/player/components/TimelineRuler.tsx
@@ -1,9 +1,10 @@
 import { memo } from "react";
 import type { TimelineTheme } from "./timelineTheme";
-import { RULER_H, formatTimelineTickLabel } from "./timelineLayout";
+import { RULER_H, formatTimelineTickLabel, getTimelineBeatEntries } from "./timelineLayout";
 import { usePlayerStore } from "../store/playerStore";
 import { secondsToFrame } from "../lib/time";
 import type { MusicBeatAnalysis } from "@hyperframes/core/beats";
+import type { TimelineTimeRange } from "../lib/timelineClipIndex";
 
 interface TimelineRulerProps {
   major: number[];
@@ -16,6 +17,7 @@ interface TimelineRulerProps {
   theme: TimelineTheme;
   beatAnalysis?: MusicBeatAnalysis | null;
   contentOrigin: number;
+  renderTimeRange?: TimelineTimeRange;
 }
 
 export const TimelineRuler = memo(function TimelineRuler({
@@ -29,10 +31,12 @@ export const TimelineRuler = memo(function TimelineRuler({
   theme,
   beatAnalysis,
   contentOrigin,
+  renderTimeRange,
 }: TimelineRulerProps) {
   const timeDisplayMode = usePlayerStore((s) => s.timeDisplayMode);
   const beatTimes = beatAnalysis?.beatTimes ?? [];
   const beatStrengths = beatAnalysis?.beatStrengths ?? [];
+  const beatEntries = getTimelineBeatEntries(beatTimes, beatStrengths, renderTimeRange);
 
   // Only draw beat lines when they'd be at least 5px apart
   const avgBeatInterval =
@@ -51,13 +55,14 @@ export const TimelineRuler = memo(function TimelineRuler({
         height={totalH}
       >
         {showBeats &&
-          beatTimes.map((t, i) => {
+          beatEntries.map(({ time: t, index: i, strength: beatStrength }) => {
             const x = t * pps;
             // Louder beats → brighter line. Gamma curve widens the contrast.
-            const strength = Math.pow(Math.min(1, beatStrengths[i] ?? 0.5), 2.2);
+            const strength = Math.pow(Math.min(1, beatStrength ?? 0.5), 2.2);
             const opacity = 0.08 + strength * 0.62;
             return (
               <line
+                data-timeline-grid-cell="beat"
                 key={`b-${t}-${i}`}
                 x1={x}
                 y1={0}
@@ -103,13 +108,23 @@ export const TimelineRuler = memo(function TimelineRuler({
               contentOrigin + t * pps (see getTimelinePlayheadLeft). Without the shift
               a tick spans [x, x+1) and its center is half a pixel right. */}
           {minor.map((t) => (
-            <div key={`m-${t}`} className="absolute bottom-0" style={{ left: t * pps - 0.5 }}>
+            <div
+              key={`m-${t}`}
+              data-timeline-grid-cell="minor"
+              className="absolute bottom-0"
+              style={{ left: t * pps - 0.5 }}
+            >
               <div className="w-px h-2" style={{ background: theme.tickMinor }} />
             </div>
           ))}
 
           {major.map((t) => (
-            <div key={`M-${t}`} className="absolute top-0" style={{ left: t * pps - 0.5 }}>
+            <div
+              key={`M-${t}`}
+              data-timeline-grid-cell="major"
+              className="absolute top-0"
+              style={{ left: t * pps - 0.5 }}
+            >
               <span
                 className="absolute font-mono tabular-nums leading-none whitespace-nowrap"
                 style={{

diff --git a/packages/studio/src/player/components/timelineLayout.test.ts b/packages/studio/src/player/components/timelineLayout.test.ts
@@ -14,7 +14,47 @@ import {
   getTimelineRowGeometry,
   trackHeights,
   resolveTimelineAssetDrop,
+  generateTicks,
+  getTimelineBeatEntries,
+  getTimelineMajorTickInterval,
 } from "./timelineLayout";
+import { getTimelineRenderTimeRange } from "./timelineViewportGeometry";
+
+describe("horizontal timeline window", () => {
+  it("adds the shared half-viewport overscan on each side and clamps to duration", () => {
+    expect(getTimelineRenderTimeRange({ scrollLeft: 300, clientWidth: 500 }, 100, 200, 20)).toEqual(
+      { start: 0, end: 8.5 },
+    );
+    expect(
+      getTimelineRenderTimeRange({ scrollLeft: 1_900, clientWidth: 500 }, 100, 200, 20),
+    ).toEqual({ start: 14.5, end: 20 });
+  });
+
+  it("generates globally aligned ticks directly inside the bounded window", () => {
+    const ticks = generateTicks(10_000, 100, undefined, { start: 500.2, end: 501.8 });
+    const interval = getTimelineMajorTickInterval(10_000, 100);
+    expect(ticks.major.every((time) => time >= 500.2 && time <= 501.8)).toBe(true);
+    expect(
+      ticks.major.every((time) => Math.abs(time / interval - Math.round(time / interval)) < 1e-6),
+    ).toBe(true);
+    expect(ticks.major.length + ticks.minor.length).toBeLessThan(100);
+  });
+
+  it("slices beat records with original strength indexes and unions a pinned beat", () => {
+    expect(
+      getTimelineBeatEntries(
+        [0, 1, 2, 3],
+        [0.1, 0.2, 0.3, 0.4],
+        { start: 1, end: 3 },
+        new Set([3]),
+      ),
+    ).toEqual([
+      { index: 1, time: 1, strength: 0.2 },
+      { index: 2, time: 2, strength: 0.3 },
+      { index: 3, time: 3, strength: 0.4 },
+    ]);
+  });
+});
 
 describe("variable timeline row geometry", () => {
   const tracks = [

diff --git a/packages/studio/src/player/components/timelineLayout.ts b/packages/studio/src/player/components/timelineLayout.ts
@@ -1,6 +1,11 @@
 import type { ZoomMode } from "../store/playerStore";
+import type { TimelineTimeRange } from "../lib/timelineClipIndex";
 
-export { formatTimelineTickLabel, generateTicks } from "./timelineRulerGeometry";
+export {
+  formatTimelineTickLabel,
+  generateTicks,
+  getTimelineMajorTickInterval,
+} from "./timelineRulerGeometry";
 
 /* ── Layout constants ──────────────────────────────────────────────── */
 export const GUTTER = 32;
@@ -11,6 +16,47 @@ export const RULER_H = 24;
 export const CLIP_Y = 3;
 export const CLIP_HANDLE_W = 18;
 
+export interface TimelineBeatEntry {
+  readonly index: number;
+  readonly time: number;
+  readonly strength: number | undefined;
+}
+
+function findFirstTimeAtOrAfter(times: readonly number[], target: number): number {
+  let low = 0;
+  let high = times.length;
+  while (low < high) {
+    const mid = Math.floor((low + high) / 2);
+    if ((times[mid] ?? Number.POSITIVE_INFINITY) < target) low = mid + 1;
+    else high = mid;
+  }
+  return low;
+}
+
+/** Slice sorted beat data without allocating entries outside the render window. */
+export function getTimelineBeatEntries(
+  beatTimes: readonly number[] | undefined,
+  beatStrengths: readonly number[] | undefined,
+  range: TimelineTimeRange | undefined,
+  pinnedIndexes: ReadonlySet<number> = new Set(),
+): readonly TimelineBeatEntry[] {
+  if (!beatTimes?.length) return [];
+  const start = range?.start ?? Number.NEGATIVE_INFINITY;
+  const end = range?.end ?? Number.POSITIVE_INFINITY;
+  const selected = new Set<number>();
+  for (let index = findFirstTimeAtOrAfter(beatTimes, start); index < beatTimes.length; index++) {
+    const time = beatTimes[index];
+    if (time === undefined || time >= end) break;
+    selected.add(index);
+  }
+  for (const index of pinnedIndexes) {
+    if (index >= 0 && index < beatTimes.length) selected.add(index);
+  }
+  return [...selected]
+    .sort((left, right) => left - right)
+    .map((index) => ({ index, time: beatTimes[index]!, strength: beatStrengths?.[index] }));
+}
+
 export function getTimelineLaneTop(laneIndex: number): number {
   return TRACK_H + Math.max(0, Math.trunc(laneIndex)) * LANE_H;
 }

diff --git a/packages/studio/src/player/components/timelineRulerGeometry.ts b/packages/studio/src/player/components/timelineRulerGeometry.ts
@@ -1,7 +1,8 @@
 import { formatTime } from "../lib/time";
+import type { TimelineTimeRange } from "../lib/timelineClipIndex";
 
 // fallow-ignore-next-line complexity
-function getTimelineMajorTickInterval(
+export function getTimelineMajorTickInterval(
   duration: number,
   pixelsPerSecond?: number,
   frameRate?: number,
@@ -49,28 +50,54 @@ function roundTickValue(time: number): number {
   return Math.round(time * 1e6) / 1e6;
 }
 
+function isSupportedTickDuration(duration: number): boolean {
+  return duration > 0 && Number.isFinite(duration) && duration <= 14400;
+}
+
+function getTickRange(duration: number, range?: TimelineTimeRange): TimelineTimeRange {
+  return {
+    start: Math.max(0, range?.start ?? 0),
+    end: Math.min(duration, range?.end ?? duration),
+  };
+}
+
+function appendMinorTicks(
+  minor: number[],
+  majorTime: number,
+  minorInterval: number,
+  subdivisions: number,
+  range: TimelineTimeRange,
+  maxTicks: number,
+  majorCount: number,
+): void {
+  for (let part = 1; part < subdivisions && majorCount + minor.length < maxTicks; part++) {
+    const time = majorTime + part * minorInterval;
+    if (time >= range.start - 0.001 && time <= range.end + 0.001) {
+      minor.push(roundTickValue(time));
+    }
+  }
+}
+
 export function generateTicks(
   duration: number,
   pixelsPerSecond?: number,
   frameRate?: number,
+  range?: TimelineTimeRange,
 ): { major: number[]; minor: number[] } {
-  if (duration <= 0 || !Number.isFinite(duration) || duration > 14400) {
-    return { major: [], minor: [] };
-  }
+  if (!isSupportedTickDuration(duration)) return { major: [], minor: [] };
   const majorInterval = getTimelineMajorTickInterval(duration, pixelsPerSecond, frameRate);
   const subdivisions = getMinorSubdivisions(majorInterval, pixelsPerSecond, frameRate);
   const minorInterval = subdivisions > 0 ? majorInterval / subdivisions : 0;
   const major: number[] = [];
   const minor: number[] = [];
   const maxTicks = 2000;
-  for (let index = 0; major.length < maxTicks; index++) {
+  const tickRange = getTickRange(duration, range);
+  const firstMajorIndex = Math.max(0, Math.floor(tickRange.start / majorInterval));
+  for (let index = firstMajorIndex; major.length < maxTicks; index++) {
     const time = index * majorInterval;
-    if (time > duration + 0.001) break;
-    major.push(roundTickValue(time));
-    for (let part = 1; part < subdivisions && major.length + minor.length < maxTicks; part++) {
-      const minorTime = time + part * minorInterval;
-      if (minorTime <= duration + 0.001) minor.push(roundTickValue(minorTime));
-    }
+    if (time > tickRange.end + 0.001) break;
+    if (time >= tickRange.start - 0.001) major.push(roundTickValue(time));
+    appendMinorTicks(minor, time, minorInterval, subdivisions, tickRange, maxTicks, major.length);
   }
   return { major, minor };
 }

diff --git a/packages/studio/src/player/components/timelineViewportGeometry.ts b/packages/studio/src/player/components/timelineViewportGeometry.ts
@@ -1,6 +1,26 @@
 import { RULER_H, type TimelineRowGeometry } from "./timelineLayout";
+import { TIMELINE_VIEWPORT_BUDGETS } from "../lib/timelineViewportBudgets";
+import type { TimelineTimeRange } from "../lib/timelineClipIndex";
 import type { TimelineScrollViewportSnapshot } from "./useTimelineScrollViewport";
 
+export function getTimelineRenderTimeRange(
+  viewport: Pick<TimelineScrollViewportSnapshot, "scrollLeft" | "clientWidth">,
+  pixelsPerSecond: number,
+  contentOrigin: number,
+  duration: number,
+): TimelineTimeRange {
+  if (!(pixelsPerSecond > 0) || !(duration > 0) || !(viewport.clientWidth > 0)) {
+    return { start: 0, end: 0 };
+  }
+  const overscanPx = viewport.clientWidth * TIMELINE_VIEWPORT_BUDGETS.timeOverscanViewportRatio;
+  const startPx = viewport.scrollLeft - contentOrigin - overscanPx;
+  const endPx = viewport.scrollLeft + viewport.clientWidth - contentOrigin + overscanPx;
+  return {
+    start: Math.min(duration, Math.max(0, startPx / pixelsPerSecond)),
+    end: Math.min(duration, Math.max(0, endPx / pixelsPerSecond)),
+  };
+}
+
 export function getTimelineVisibleTimeRange(
   viewport: Pick<TimelineScrollViewportSnapshot, "scrollLeft" | "clientWidth">,
   pixelsPerSecond: number,