Section Repeat for YouTube™

1. Overview

The ultimate tool for musicians, dancers, language learners, and anyone who needs to master specific parts of a video.

Section Repeat for YouTube™ is a browser extension engineered to enhance practice and learning efficiency on the YouTube platform. It provides a keyboard-driven interface for slicing and repeating of video segments. It enables A-B repeat style practice by looping user-defined clips, prioritizing a streamlined, mouse-free experience for music, dance, and language learning.

2. Core Principles

This extension is built on three core principles:

🔒 Privacy First: We do not collect, store, or share any of your personal data. Everything happens on your computer, and we have no access to your viewing history or activity.
⚡️ Performance-Oriented: Built with modern Manifest V3 standards and VanillaJS, the extension is designed for minimal impact on browser resources. It is lightweight and fast, with no external frameworks.
⌨️ Keyboard-Centric: All core functions are designed to be controlled entirely without a mouse, allowing you to stay focused on your practice without interrupting your workflow.

3. Key Features

🎯 Precision Slicing: Define multiple, high-precision video sections with a single key press.
⌨️ Keyboard-Centric Workflow: All core functions are mapped to intuitive shortcuts for maximum efficiency, allowing you to maintain your workflow without a mouse.
🔁 Seamless Navigation & Repeat: Instantly navigate between sections and toggle repeat mode with simple key presses.
✨ Intelligent Automation:
- Auto-Looping: When a video with defined sections ends, repeat mode automatically starts from the first section.
- Focus Mode: A dedicated shortcut reloads a video from a playlist into a standalone player, preventing auto-play from interrupting your practice sessions.
- Error Prevention: Incomplete sections are automatically completed or discarded, ensuring a seamless transition into repeat mode without data errors.

4. Getting Started

Installation

From the Chrome Web Store (Recommended)
- Install Here
Manual Installation (for Developers)

Click to view installation instructions

1. Clone this repository or download and unzip the source code. 2. Open Chrome and navigate to `chrome://extensions`. 3. Enable "Developer mode" in the top-right corner. 4. Click "Load unpacked" and select the project's root directory.

Quick Start

Make a section: press S to start and E to end.
Chain sections: press E again to add the next section.
Repeat & Navigate: press R to toggle repeat; press A or D to move between sections.

Shortcuts

All core functions of the extension are controlled by the shortcuts below.

Key	Action	Description
S	Start section	Sets the start-time for a new section.
E	End section	Completes the current section. Press again to start the next section where the last one ended.
R	Toggle Repeat	Starts or stops repeating through the defined sections.
A / D	Previous / Next section	Moves to the previous (`A`) or next (`D`) section and begins repeating automatically.
1-9	Jump to section	Instantly jumps to a specific section (1 through 9).
W	Enter Focus Mode	In a playlist, reloads the video in a standalone view to prevent auto-advancing.
Q	Clear all sections	Deactivates all extension functions and clears all sections for the current video.

5. Technical Architecture

Core Logic: Vanilla JavaScript, compliant with the Manifest V3 standard.
State Management: chrome.storage.session is used for temporary data that is cleared when a tab is closed, while chrome.storage.sync is used for a privacy-protecting security key (salt). Section data itself is stored in chrome.storage.local.
DOM Interaction: A single, unified MutationObserver monitors the YouTube player, with debouncing and filtering to minimize performance impact. DOM lookups are optimized via an LRUCache.
UI Components: Toasts and overlays render in isolated Shadow DOM trees to prevent style conflicts with the host page.
Security: Locally stored video IDs are hashed with a user-specific salt using the SubtleCrypto API. The extension makes no external network requests.

6. Technical Specifications

Section & Storage Limits:
- Max Sections per Video: 50
- Min Section Duration: 0.5 seconds
- Data Expiration: Sections unused for 30+ days are subject to cleanup.
- Max Total Keys: 3,000
- Storage Quota: 5MB (chrome.storage.local)
Storage Cleanup:
- Automatic Purge: Runs every 60 minutes to clear expired data.
- User Notifications: A toast notification is shown when storage usage exceeds 75%, and a manual cleanup button appears in the popup when usage exceeds 90%.

7. Project Information

Author: Eunjeong Song (Homepage / LinkedIn)
Source Code: GitHub Repository
Privacy & Legal:
- Privacy Policy: Read our Privacy Policy
- Changelog: View release notes
- License: This project is licensed under the PolyForm Noncommercial License 1.0.0. This means the software may be freely used, copied, modified, and distributed for noncommercial purposes only. For commercial use, please contact the author.
- Disclaimer: Section Repeat for YouTube™ is an independent project and is not officially associated with YouTube or Google LLC. “YouTube” is a trademark of Google LLC.
Acknowledgements: Icon by khulqi Rosyid from IconFinder (CC BY 4.0).