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Interval Timer App: Smart Interval Timer for Physical Therapy & Workouts

Interval Timer App is a modern, responsive web application designed specifically for physical therapy routines, mobility protocols, and interval training. It offers precise multi-set and multi-rep timing, unilateral (left/right side) exercise alternation, multimedia posture lightboxes, Edge-TTS audio cues, hands-free voice commands, and a floating Picture-in-Picture countdown.

Overview

Unlike generic gym timers that only cycle through basic work/rest countdowns, the Interval Timer App is built from the ground up to accommodate structured physical therapy and rehabilitation programs. It supports detailed exercise configurations (sets, reps, intra-rep rest, inter-set rest), unilateral left/right tracking, media guidance (posture images and YouTube video embeds), hands-free voice control when on an exercise mat, and post-session pain tracking to monitor physical recovery over time.

Key Features

1. Workout & Exercise Engine

  • Configurable Interval Hierarchy: Set custom work durations, rest between reps, rest between sets, preparation buffers, and exercise notes.
  • Unilateral / Two-Sided Exercise Support: Automatically alternates between Left Side and Right Side with dedicated voice transitions ("Left side first", "Switch sides").
  • Exercise Management: Drag-free reordering (move up/down) and 1-click exercise cloning.
  • Skip & Scrub Controls: Jump between exercises or step backward/forward through workout phases on the fly.

2. Visual & Timer Interface

  • Animated SVG Countdown Ring: Smooth, color-coded circular timer (Amber for Prepare, Green for Work, Red for Rest).
  • Overall Workout Progress: Real-time progress bar tracking total elapsed workout percentage alongside active exercise numbers.
  • 1-Tap Fullscreen Mode: Distraction-free, high-contrast timer view for desktop screens, wall-mounted tablets, or phones.
  • Picture-in-Picture (PiP) Floating Window: Float an active countdown window over other applications, allowing you to follow along while reading articles or watching videos.

3. Audio, Voice & Hands-Free Interaction

  • Edge-TTS Voice Prompts: Natural-sounding speech announcements ("3-2-1 Go", "Rest", "Prepare for next exercise") powered by Microsoft Edge TTS.
  • Audio & Haptic Customization: Configurable prompt verbosity (Full, Minimal, Muted), speech rate scaling (\(0.8\times - 1.4\times\)), audio beeps, and mobile vibration feedback.
  • Hands-Free Voice Recognition: Speak commands ("Pause", "Resume", "Next", "Back", "Skip") with a live HUD indicator—ideal when holding planks or floor stretches.

4. Multimedia Posture & Form Lightbox

  • Clickable Media Lightbox: Click any exercise thumbnail in the plan builder or workout screen to launch full-resolution posture diagrams or image carousels.
  • YouTube Embed Support: Embed video tutorials directly into exercise cards with auto-fetched thumbnail previews.
  • Aspect Ratio Containment: Uncropped image rendering (object-fit: contain) ensures posture diagrams and anatomical callouts are never cut off.

5. Health Tracking, Analytics & Motivation

  • Pain Level Tracker (0–10 Scale): Log post-session pain scores with emoji mood indicators and clinical notes.
  • Pain Trend Sparkline: Interactive recovery trend line in the Stats modal to track discomfort reduction across days and weeks.
  • 30-Day Activity Heatmap: Visual contribution grid tracking workout frequency and consistency.
  • Streak Counters: Displays current active streaks and total completion metrics.

6. Data Portability & PWA

  • Curated Routine Presets: Built-in starter routines (Shoulder & Neck PT, Core & Planks, Desk Ergonomics, 7-Min HIIT).
  • Import / Export: Seamless backup and cross-device sharing via .yml or .json files, plus an in-app raw YAML editor.
  • Progressive Web App (PWA): Installable on iOS, Android, macOS, and Windows with offline media caching.
  • Screen Wake Lock API: Prevents your device screen from dimming or locking during workout sessions.

Installation & Setup

Deploy the service with the following docker-compose.yml:

version: '3.8'

services:
  interval-timer-app:
    image: ghcr.io/binuengoor/interval-timer-app:latest
    container_name: interval-timer-app
    ports:
      - "8080:80"
    volumes:
      - ./data:/app/data
    restart: unless-stopped

Start the container: 

docker compose up -d

Access the application in your browser at http://<your-server-ip>:8080.

Option 2: Docker Run

docker run -d \
  --name interval-timer-app \
  -p 8080:80 \
  -v $(pwd)/data:/app/data \
  --restart unless-stopped \
  ghcr.io/binuengoor/interval-timer-app:latest

Option 3: Local Development (Node.js)

# Clone the repository
git clone https://github.com/binuengoor/interval-timer-app.git
cd interval-timer-app

# Install dependencies
npm install

# Start the Node.js server
npm start

Open http://localhost:8080 in your web browser.

Data Persistence & Directory Structure

When running via Docker, bind-mount the ./data directory to persist routines and analytics:

data/
├── plans.yml       # Stores all custom and imported workout routines
└── stats.yml       # Stores completed session logs, streaks, and pain ratings
  • plans.yml: Contains structured YAML definitions for all your workout plans. You can edit this file directly or through the app's YAML editor.
  • stats.yml: Tracks completion dates, durations, pain levels, and notes for historical analytics.

Keyboard Shortcuts (Workout View)

Key Action
Space Toggle Play / Pause
→ Advance to Next Phase / Step
← Return to Previous Phase / Step
Esc Close active modal, stats, or media lightbox

Technical Details

  • Backend: Node.js, Express.js, node-edge-tts (Microsoft Edge TTS synthesis), js-yaml (YAML parsing/serialization), and axios.
  • Frontend: Modern Vanilla JavaScript, responsive CSS with Dark Mode styling, SVG circular progress rendering, and Web Audio API synthesis.
  • APIs Used:
    • Screen Wake Lock API: Keeps display active throughout workouts.
    • Web Speech API: Powers hands-free voice command recognition and fallback speech synthesis.
    • Picture-in-Picture API: Renders canvas countdown to a floating OS window.
    • Service Worker & Workbox: Enables offline PWA caching.

Troubleshooting

  • Voice Prompts Not Playing: Ensure your browser permissions allow audio playback. Some mobile browsers require an initial user interaction (e.g., pressing "Start") before playing Web Audio or TTS streams.
  • Voice Commands Not Listening: Check browser microphone permissions. Voice recognition requires an active microphone connection and is supported on Chromium-based browsers (Chrome, Edge, Brave) and Safari.
  • Screen Dimming During Workout: Verify that your browser supports the Screen Wake Lock API (enabled by default on modern Chrome, Edge, and Safari).
  • Data Not Persisting: Ensure the ./data host directory has proper read/write permissions for the container process.