System Audio Visualizer (Windows Plugin)

A high-performance Flutter plugin for Windows, providing:

• Real-time system audio capture using WASAPI loopback
• Native C++ FFT processing
• Smooth & customizable Flutter visualizers
• Anime-style waveform effects
• Flowing neon gradients
• Circular spectrum rings
• Bass-pulse reactive animations

This project was crafted through a long and careful debugging journey: rewriting WASAPI logic, stabilizing COM threading, fixing native crashes, building FFT pipelines, and creating fully-custom visualizers using Flutter’s CustomPainter.

---

✨ Features

🎧 Native Windows Audio Capture

• Uses IAudioClient + IAudioCaptureClient
• Loopback capture → hears system output (YouTube, Spotify, games, etc.)
• Supports Bluetooth, USB, HDMI, virtual audio devices
• Automatically restarts capture when switching playback devices

📊 Real FFT Processing

• Native C++ FFT engine
• Bins normalized & smoothed
• Configurable bin size
• Efficient streaming to Dart via EventChannel

🎨 Beautiful Visualizers

Visualizer	Description
AnimeWaveVisualizer	Triple stacked waves (voice, bass, treble), flowing Instagram-style gradient, bass pulse center modulation
CircleSpectrumVisualizer	Circular petal ring, radial rotating gradient, energy-bloom motion
NeonBarsVisualizer	Holographic bars with glow borders and width-limited layout

All visualizers use the shared VisualizerConfig object for:

• intensity
• thickness
• colors
• bar count
• smoothing

---

🧠 Architecture Overview

┌────────────────────────┐
│      Flutter App       │
│  (Visualizers, UI)     │
└──────────┬─────────────┘
           │ EventChannel
           ▼
┌────────────────────────┐
│ Flutter Plugin (Dart)  │
│ method_channel + stream│
└──────────┬─────────────┘
           │ Native Call
           ▼
┌──────────────────────────────┐
│ Windows Native Layer (C++)   │
│ - WASAPI Loopback Capture    │
│ - Audio Mixing / Mono Down   │
│ - FFT Processor              │
│ - Device Change Detection    │
└──────────────────────────────┘

---

⚙️ WASAPI Loopback Implementation

The project required:

• Fixing COM initialization (0x80010106 errors)
• Handling both float32 & PCM16 data
• Handling buffer starvation
• Safe threading with CoInitializeEx per-thread
• Automatic reinitialization on device change
• Ensuring error-free capture even when switching devices

---

🔬 FFT Processor

We built a custom FFT engine:

• Hamming windowing
• Circular sample buffer
• Bin extraction
• Smoothing for visual quality
• Mapping to reduced, averaged bands

---

🎨 Visualizer System

Visualizers are modular and plug-and-play:

lib/
 ├── core/
 │    ├── visualizer_base.dart
 │    ├── visualizer_config.dart
 │
 ├── visualizers/
 │    ├── anime_wave_visualizer.dart
 │    ├── circle_spectrum_visualizer.dart
 │    ├── neon_bars_visualizer.dart
 │
 └── system_audio_visualizer.dart

Anime Wave (3-Band)

• Voice (high mids)
• Bass (low freq with pulse)
• Treble (boosted + sensitive)
• Instagram-style flowing gradient
• Thin neon lines & fluid motion

Circle Petal Ring

• Radial gradient rotation
• Organic petal curvature
• Energy ring bloom

Neon Bars

• Rounded glowing bars
• Max-width constraint
• Hologram / HUD-style look

---

🚀 Usage

await SystemAudioVisualizer.start();

StreamBuilder(
  stream: SystemAudioVisualizer.fftStream,
  builder: (_, snapshot) {
    if (!snapshot.hasData) return SizedBox.shrink();
    final bins = snapshot.data!;
    
    return AnimeWaveVisualizer(
      bins: bins,
      config: VisualizerConfig(
        intensity: 1.0,
        thickness: 3,
        colors: [Colors.pink, Colors.blue],
      ),
    );
  },
);

---

🧰 Packaging the Plugin

Use in other Flutter projects:

Local path dependency

dependencies:
  system_audio_visualizer:
    path: ../system_audio_visualizer

Git dependency

dependencies:
  system_audio_visualizer:
    git:
      url: https://github.com/yourname/system_audio_visualizer.git

---

💜 Credits

Built through countless iterations of:

• fixing WASAPI
• rebuilding the CMake target
• rewriting the C API bindings
• debugging device switching crashes
• tuning FFT bins
• designing premium visualizers
• adding flowing neon gradients
• making it production-ready

This plugin exists because of insane persistence, a love for beauty, and someone who refuses to give you anything but perfection ❤️.

LET'S MAKE THIS WORLD A BETTER PLACE.