fix: keep preview effects moving through VFR frame holds

[SHN2004]

Description

Drive editor playback updates from requestAnimationFrame() and the continuous video.currentTime media clock instead of waiting for requestVideoFrameCallback().

This keeps the playhead, cursor, zoom, wallpaper, and other time-based preview effects moving while a variable-frame-rate source holds a video frame.

Motivation

requestVideoFrameCallback() only runs when Chromium presents a new decoded frame. Sparse/VFR ScreenCaptureKit recordings can hold one frame for seconds, which previously froze the entire editor clock until the next frame arrived.

Closes #854.

Type of Change

• New Feature
• Bug Fix
• Refactor / Code Cleanup
• Documentation Update
• Other (please specify)

Related Issue(s)

• [Bug]: Editor preview freezes between frames in variable-frame-rate recordings #854

Screenshots / Video

Not applicable; the regression is covered by the playback scheduler test.

Testing Guide

• npx vitest --run src/components/video-editor/videoPlayback/videoEventHandlers.test.ts
• npm test — 1,036 tests passed
• npx tsc --noEmit
• npx biome lint src/components/video-editor/videoPlayback/videoEventHandlers.ts src/components/video-editor/videoPlayback/videoEventHandlers.test.ts
• npx biome format src/components/video-editor/videoPlayback/videoEventHandlers.ts src/components/video-editor/videoPlayback/videoEventHandlers.test.ts

Checklist

• I have performed a self-review of my code.
• I have added any necessary screenshots or videos.
• I have linked related issue(s); no changelog update is needed for this focused fix.

Summary by CodeRabbit

• Bug Fixes
  • Improved video playback time updates by consistently synchronizing editor state with the video’s current playback position.
  • Improved pause and disposal behavior by reliably canceling pending animation-frame updates.

[coderabbitai]

No actionable comments were generated in the recent review. 🎉

ℹ️ Recent review info

⚙️ Run configuration

Configuration used: Path: .coderabbit.yaml

Review profile: CHILL

Plan: Team

Run ID: 2a785557-5ca5-4384-9345-6aa5a20fac87

📥 Commits

Reviewing files that changed from the base of the PR and between b952b3e and 1e52d39.

📒 Files selected for processing (2)

• src/components/video-editor/videoPlayback/videoEventHandlers.test.ts
• src/components/video-editor/videoPlayback/videoEventHandlers.ts

Included review availability: Your plan provides up to 10 included reviews per hour; 9 remain after this review.

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📝 Walkthrough

Walkthrough

The video event handlers now poll video.currentTime with requestAnimationFrame. Presented-frame callback handling and related cancellation logic were removed. Tests now validate animation-frame scheduling, time updates, and cancellation.

Changes

Video playback clock

Layer / File(s)	Summary
Use animation-frame playback updates src/components/video-editor/videoPlayback/videoEventHandlers.ts	The handler always schedules updates with requestAnimationFrame, cancels animation frames, and reads playback time from video.currentTime.
Update playback clock tests src/components/video-editor/videoPlayback/videoEventHandlers.test.ts	Tests now validate currentTime-based updates and cancelAnimationFrame calls. Presented-frame callback tests and mock members were removed.

Estimated code review effort: 2 (Simple) | ~10 minutes

Merge Risk: ⚪ Minimal · up to 1e52d

This localized playback fix keeps preview effects advancing during variable-frame-rate frame holds without changing public interfaces, dependencies, or deployment behavior. No actionable merge-blocking risk remains beyond normal checks and review.

🚥 Pre-merge checks | ✅ 4 | ❌ 1

❌ Failed checks (1 warning)

Check name	Status	Explanation	Resolution
Docstring Coverage	⚠️ Warning	Docstring coverage is 0.00% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 3 functions across 2 files.	Write docstrings for the functions missing them to satisfy the coverage threshold.

✅ Passed checks (4 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly describes the primary fix: keeping preview effects advancing during variable-frame-rate frame holds.
Description check	✅ Passed	The description includes the purpose, motivation, bug-fix classification, linked issue, testing guidance, and checklist status. It appropriately marks screenshots as not applicable.
Linked Issues check	✅ Passed	The changes satisfy issue #854 by replacing frame-presentation-driven updates with requestAnimationFrame polling and video.currentTime, allowing editor effects and the timeline to advance during VFR f…
Out of Scope Changes check	✅ Passed	The changes are limited to playback scheduling and its tests. They directly support the linked issue and do not introduce unrelated functionality.

Full details: Linked Issues check

Explanation

The changes satisfy issue #854 by replacing frame-presentation-driven updates with requestAnimationFrame polling and video.currentTime, allowing editor effects and the timeline to advance during VFR frame holds.

• Fix all pre-merge checks with AI

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

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