ChronoBeat-IO

Internet-Based Synchronized Audio Playback — Beat-level sync across multiple devices without WebSockets.

Live Demo — Try it now!

Overview

ChronoBeat-IO enables synchronized music playback between multiple devices without WebSockets, by anchoring audio playback to a global server time instead of relying on real-time message delivery.

The goal is perceptual beat-level sync (like an add-on speaker), not sample-perfect hardware sync. All connected devices play the same track at the same global timestamp, creating seamless multi-device listening experiences.

Key Innovation

Instead of synchronizing play / pause events, all devices synchronize time.

Every device plays the same track at the same global timestamp.

Visuals

Features

[+] Multi-Device Synchronization — Sync music playback across unlimited devices in real-time
[+] WebSocket-Free — Uses stateless REST HTTP APIs for maximum compatibility
[+] NTP-Style Time Sync — Client clocks auto-calibrate for accuracy
[+] Drift Correction — Automatic periodic correction for clock drift
[+] Room-Based Architecture — Create multiple independent listening rooms
[+] Leader/Follower Model — One user controls playback, others follow seamlessly
[+] Audio Upload & Streaming — Upload MP3/WAV files or stream from URLs
[+] User Management — Track connected users with avatars and IDs
[+] Volume Control & Muting — Individual device volume control
[+] Real-Time User List — See who's connected in your room
[+] Progressive Web App — Works on desktop and mobile
[+] Dark Mode UI — Beautiful Material Design interface

Technology Stack

Frontend

React 19.2 — UI framework
Vite 7.2 — Fast build tool
Material-UI 7.3 — Component library
React Router 7.10 — Routing
Tailwind CSS 4.1 — Utility-first styling

Backend

Node.js + Express 5.2 — REST API server
Multer 2.0 — File upload handling
CORS 2.8 — Cross-origin requests

Infrastructure

Render — Deployment platform (see RENDER_DEPLOYMENT.md)
HTTP/REST — Stateless API design

System Architecture

Time Synchronization (Critical Step)

Client clocks are not trusted directly. Each device estimates its offset from server time using an NTP-style exchange:

offset = serverTime - clientLocalTime

This offset is stored locally and applied to all playback calculations.

Playback Anchor Model

When a leader starts playback, the system creates a playback anchor:

{
  "trackUrl": "song.mp3",
  "songPositionMs": 4534,
  "serverTimeMs": 1723456789267,
  "isPlaying": true
}

This anchor is the single source of truth for all connected devices.

Playback Calculation (Follower Device)

When a device receives the playback anchor later than the leader:

nowServerTime = Date.now() + offset
elapsed = nowServerTime - anchor.serverTimeMs
startPositionSec = (anchor.songPositionMs + elapsed) / 1000

Playback starts from the calculated position:

audio.currentTime = startPositionSec
audio.play()

This ensures beat alignment, even if playback begins mid-track.

Drift Correction (Maintaining Sync)

Clock drift and decoding differences are corrected periodically.

Every 2–3 seconds:

expected = (Date.now() + offset - serverStartTime) / 1000
drift = audio.currentTime - expected

if (Math.abs(drift) > 0.12) {
  audio.currentTime = expected
}

Small corrections keep devices perceptually synchronized over long sessions.

Getting Started

Prerequisites

Node.js 16+ and npm
Modern web browser with Web Audio API support

Installation

Clone the repository

git clone https://github.com/yourusername/ChronoBeat-IO.git
cd ChronoBeat-IO

Install dependencies

# Frontend dependencies
npm install

# Backend dependencies
cd server
npm install
cd ..

Start development servers

Open two terminals:

Terminal 1 - Frontend (Vite)

npm run dev

Frontend runs on http://localhost:5173

Terminal 2 - Backend (Express)

cd server
npm start

Backend runs on http://localhost:3000

Open in browser Navigate to http://localhost:5173 and start creating rooms!

Live Deployment

The application is deployed and accessible at:

Frontend: https://chronobeat-frontend.onrender.com
Backend: https://chronobeat-backend.onrender.com (or your configured URL)

You can start using it immediately without local setup!

Build for Production

# Frontend build
npm run build

# Outputs to dist/ directory

Project Structure

ChronoBeat-IO/
├── src/
│   ├── components/
│   │   ├── AudioSelector.jsx      # Audio file/URL selection UI
│   │   └── UserList.jsx            # Connected users display
│   ├── hooks/
│   │   ├── useTimeSync.js          # NTP-style time synchronization
│   │   ├── useAudioPreloader.js    # Audio file preloading
│   │   ├── useSyncedAudio.js       # Core playback sync logic
│   │   ├── useRoom.js              # Room state management
│   │   ├── useScheduledAudio.js    # Scheduled playback
│   │   └── useWebRTC.js            # WebRTC signaling (future)
│   ├── pages/                       # Route pages
│   ├── App.jsx                      # Main React component
│   ├── main.jsx                     # Entry point
│   └── assets/                      # Static assets
├── server/
│   ├── index.js                     # Express REST API server
│   └── package.json                 # Server dependencies
├── public/                          # Static files
├── index.html                       # HTML entry point
├── vite.config.js                   # Vite configuration
├── eslint.config.js                 # Linting rules
├── package.json                     # Frontend dependencies
└── README.md                         # This file

How It Works

1. Create or Join a Room

Leader creates a room (gets a room ID)
Followers join using the room ID
Server tracks all connected users

2. Upload or Select Audio

Upload an MP3/WAV file, or
Provide a URL to stream audio
Audio is stored on the server and accessible to all users in the room

3. Time Synchronization

Each device pings the /api/time endpoint
Calculates clock offset from server
Stores offset for playback calculations

4. Playback Synchronization

Leader clicks play → sends playback anchor to server
Server broadcasts anchor state to all devices
Each device calculates playback position based on:
- Server timestamp
- Audio position at anchor time
- Their clock offset
All devices start playing at the same calculated position

5. Drift Correction

Every 2-3 seconds, devices check audio drift
If drift > 120ms, resync to calculated position
Keeps all devices in perceptual sync

6. User Management

Users ping server with heartbeat every 10 seconds
Server removes inactive users after 30 seconds
If leader leaves, next user becomes new leader

API Reference

Time Synchronization

GET /api/time

Returns current server timestamp in milliseconds.

Response:

{ "time": 1723456789267 }

Room Management

Join Room

POST /api/rooms/:roomId/join
Content-Type: application/json

{
  "userId": "user123",
  "username": "Alice",
  "isLeader": false
}

Leave Room

POST /api/rooms/:roomId/leave
Content-Type: application/json

{ "userId": "user123" }

Get Room State

GET /api/rooms/:roomId/state

Ping (Heartbeat)

POST /api/rooms/:roomId/ping
Content-Type: application/json

{ "userId": "user123" }

Audio Management

Upload Audio

POST /api/rooms/:roomId/audio/upload
Content-Type: multipart/form-data

[binary audio file]

Set Current Audio

POST /api/rooms/:roomId/audio/current
Content-Type: application/json

{
  "url": "https://example.com/song.mp3",
  "filename": "song.mp3"
}

Get Current Audio

GET /api/rooms/:roomId/audio/current

Playback Control

Start Playback

POST /api/rooms/:roomId/playback/start
Content-Type: application/json

{
  "userId": "user123",
  "audioOffset": 0,
  "speed": 1.0
}

Pause Playback

POST /api/rooms/:roomId/playback/pause
Content-Type: application/json

{ "userId": "user123" }

Seek Position

POST /api/rooms/:roomId/playback/seek
Content-Type: application/json

{
  "userId": "user123",
  "position": 45000
}

Deployment

Live Production URL

Frontend: https://chronobeat-frontend.onrender.com

Production Deployment on Render

See RENDER_DEPLOYMENT.md for complete setup instructions.

Quick Summary:

Deploy backend Express server to Render Web Service
Set PUBLIC_URL and ALLOWED_ORIGINS environment variables
Deploy frontend to Render Static Site with build command npm run build
Configure frontend to point to backend URL

Environment Variables

Backend (.env file):

PORT=3000
NODE_ENV=production
PUBLIC_URL=https://your-backend.onrender.com
ALLOWED_ORIGINS=https://your-frontend.onrender.com,http://localhost:5173

Frontend (.env file):

VITE_API_URL=https://your-backend.onrender.com

Troubleshooting

Issue: Audio sync is drifting

Solution: Check network latency. Large latency (>500ms) can affect sync precision.
Solution: Restart the room to reinitialize time sync.
Solution: Ensure all devices have system time set correctly.

Issue: Users disconnecting unexpectedly

Solution: Check browser console for network errors.
Solution: Ensure ALLOWED_ORIGINS in backend includes your frontend domain.
Solution: Check if devices are behind strict firewalls.

Issue: Audio file won't play

Solution: Verify file format is MP3 or WAV.
Solution: Check file size (max 50MB).
Solution: Ensure CORS headers are correctly configured.

Issue: "Cannot connect to server"

Solution: Verify backend is running and accessible.
Solution: Check browser network tab for failed requests.
Solution: Ensure PUBLIC_URL environment variable matches your deployment URL.

Performance Considerations

Sync Precision: Typically ±100-200ms perceptual sync
Max Users Per Room: Tested with 50+ users per room
Audio Quality: Limited by client's audio playback decoder
Latency Tolerance: Works best with <500ms network latency
Server Memory: ~1-2MB per active room

Future Enhancements

WebRTC audio streaming for lower latency
Playlist management
User authentication & persistent profiles
Advanced audio visualization
Voice chat integration
Mobile app (React Native)
Offline mode with sync on reconnect

Contributing

Fork the repository
Create a feature branch (git checkout -b feature/AmazingFeature)
Commit changes (git commit -m 'Add AmazingFeature')
Push to branch (git push origin feature/AmazingFeature)
Open a Pull Request

License

This project is licensed under the ISC License - see the LICENSE file for details.

Support & Contact

Email: support@chronobeat-io.com
Bug Reports: Open an issue on GitHub
Discussions: GitHub Discussions tab

Communication Model (No WebSockets)

This system uses stateless HTTP APIs:

Action	Method
Create room	POST
Play	POST
Pause	POST
Seek	POST
Sync state	GET (polling)

Clients poll the playback state every 2–5 seconds.

Expected Accuracy

Network Conditions	Sync Accuracy
Good broadband	±50–100 ms
Mobile / average	±150 ms
Cross-region	±200 ms

This level of sync is sufficient for music listening and shared playback.

Why Perfect Sync Is Impossible

Even with timestamp anchoring, sample-perfect sync cannot be achieved due to:

Different audio decoding latencies
Browser audio buffering
Hardware clock differences
Mobile power management

This limitation applies to all internet-based playback systems.

Advantages of This Approach

Works over the public internet
No WebSockets required
Compatible with serverless platforms (Vercel)
Scales easily
Mobile browser friendly

Ideal Use Cases

Shared music listening
Add-on speaker behavior across devices
Watch / listen together apps
Lightweight real-time audio sync

Summary

Timestamp-anchored playback is the best achievable method for synchronized audio over the internet.

By synchronizing time instead of events, devices can play the same song in perceptual sync, even when joining late or experiencing network latency.

This approach mirrors the techniques used by major streaming platforms and is production-proven.

Name		Name	Last commit message	Last commit date
Latest commit History 32 Commits
public		public
server		server
src		src
.gitattributes		.gitattributes
.gitignore		.gitignore
README.md		README.md
eslint.config.js		eslint.config.js
index.html		index.html
package-lock.json		package-lock.json
package.json		package.json
start.bat		start.bat
vite.config.js		vite.config.js

daemon-001/ChronoBeat-IO

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