A lightweight userscript that adds a native A/B loop panel directly into the YouTube player — no extension, no bloat. Works with ScriptCat, Tampermonkey, and any compatible userscript manager.

• A → B loop — set two timestamps and loop between them indefinitely
• Full video loop — restart the entire video automatically on end
• Mini timeline — draggable thumbs for A, B and the playhead, with a highlighted range overlay
• Keyboard shortcuts — press A or B to set points at the current time
• Auto-update banner — the panel shows a notification when a newer version is available on GitHub
• Native look — glass-morphism panel that matches YouTube's own UI style
• Zero performance waste — RAF-based render loop with per-frame value caching; only writes to the DOM when something actually changes

Panel — A/B mode	Panel — Full video mode

A userscript manager installed in your browser. Recommended options:

Click the link below — your userscript manager will open an install prompt automatically:

→ Install YouTube A/B Loop

1. Open ScriptCat (or Tampermonkey) → Create a new script
2. Paste the contents of youtube-loop.js
3. Save (Ctrl+S)

Tip: You can set A and B while the video is playing — the loop activates immediately.

ScriptCat and Tampermonkey both check for updates automatically (once per day by default) using the @updateURL and @downloadURL directives in the script header.

When a new version is published on GitHub, a yellow "Update available" banner also appears at the bottom of the panel with a direct Install link.

To bump the version yourself, update both:

• @version in the userscript header
• CURRENT_VERSION constant in the code

tryInject()  →  inject()
                  ├── mountUI()         — injects CSS + builds DOM
                  ├── setupModeSelector()
                  ├── setupPanelToggle()
                  ├── setupLoopToggle()
                  ├── setupPointButtons()
                  ├── setupTimeline()
                  ├── setupKeyboard()
                  ├── startRenderLoop() — RAF loop, enforces A/B boundary
                  └── checkForUpdate()  — async GitHub version fetch

Navigation between YouTube videos is handled via a MutationObserver on <title> (lightweight — fires only on SPA navigations, not on every DOM change). Each page gets a fresh isolated session object — no stale state between videos.

# Clone
git clone https://github.com/Black0S/Youtube-Loop-UserScript-.git

# Edit
# youtube-loop.js is a single self-contained file — no build step required.

# Test
# Install locally via ScriptCat or Tampermonkey, open any YouTube video.

When releasing a new version:

1. Bump @version in the header (e.g. 1.0.0 → 1.1.0)
2. Bump CURRENT_VERSION constant to match
3. Push to main — ScriptCat, Tampermonkey, and the in-panel banner will all pick it up automatically

MIT © Black0S