Visualizer (Android)

A tiny Jetpack Compose demo that visualizes the device audio output using the Android Visualizer API.

It attaches to audio session 0 (global output mix) and renders:

• Waveform view (time-domain samples)
• FFT magnitude bars (frequency-domain snapshot)
• Simple metrics (sample count, RMS, peak, first bytes)

The UI is written with Jetpack Compose and organized into small composables.

Features

• VisualizerController wrapper around android.media.audiofx.Visualizer
• Global output (session 0) capture for convenience
• Waveform and FFT visualizations
• Permission handling (RECORD_AUDIO)
• Basic controls to Start/Stop capture

Requirements

• Android 7.0 (API 24) or later
• Microphone permission (RECORD_AUDIO)
• Audio playing on the device (e.g., music app) to see the visualization

How it works

• VisualizerController sets up the Visualizer with the maximum supported capture size and a reasonable capture rate (half of the device max).
• It registers OnDataCaptureListener to receive waveform and FFT byte arrays.
• The app processes those bytes in Compose to draw a waveform path and magnitude bars for FFT bins.

Key parts of the UI:

• PermissionSection asks for RECORD_AUDIO when missing.
• WaveformView draws the latest waveform as a continuous path.
• FftBarsView computes magnitude per bin and draws vertical bars.
• MetricsSection shows simple stats and a short hex-ish dump of the first bytes.
• ControlButtons exposes Start/Stop buttons.

Build & Run

1. Open the project in Android Studio (Giraffe or newer recommended) and let it sync.
2. Select a connected device or emulator running API 24+.
3. Run the app.

Or via command line:

./gradlew :app:assembleDebug

Then install the generated APK on a device.

Permissions

This app requests android.permission.RECORD_AUDIO at runtime.

Note: The Visualizer API reads audio data for visualization — it does not record or store audio.

Limitations & Notes

• Some OEMs/devices restrict or alter access to the global output mix (session 0). On such devices the visualizer may return zeros or fail to initialize.
• You need active audio playback from another app to see non-zero data.
• Bluetooth/headphones/audio effects may influence sampling output.
• The FFT values are raw magnitudes derived from interleaved real/imag bytes and are not calibrated to physical units.

KDocs

Public classes and composables are documented with KDoc in the source:

• VisualizerController (class, start/stop)
• MainActivity and VisualizerScreen
• Composables: WaveformView, FftBarsView, PermissionSection, ControlButtons, MetricsSection
• AudioSessionsTracker (placeholder)

You can browse KDocs directly in code. There is no generated site output configured for this sample.

Project Info

• Min SDK: 24
• Target/Compile SDK: 36
• Kotlin/JVM target: 11
• UI: Jetpack Compose Material 3

This is a learning/demo project — feel free to adapt it to your needs.