Audio Recording
Flutter Quick Start

Platforms

• Flutter (1.20.0+)
• Android (5.0+, API 21+)
• iOS (11.0+)

Requirements

• Flutter SDK
• Android SDK (21+)
• JDK (8+)
• Xcode (11+)
• CocoaPods

Quick Start

Setup

1. Install Flutter SDK.

2. Run flutter doctor to determine any missing requirements.

3. Add the flutter_voice_processor plugin to your app project by referencing it in pubspec.yaml:

dependencies:  
  flutter_voice_processor: ^<version>

4. Enable the proper permission for recording with the hardware's microphone on both iOS and Android:

<key>NSMicrophoneUsageDescription</key>
<string>[Permission explanation]</string>

<uses-permission android:name="android.permission.RECORD_AUDIO" />

Usage

Access the singleton instance of VoiceProcessor:

import 'package:flutter_voice_processor/flutter_voice_processor.dart';

VoiceProcessor? _voiceProcessor = VoiceProcessor.instance;

Add listeners for audio frames and errors:

VoiceProcessorFrameListener frameListener = (List<int> frame) {
    // use audio
}

VoiceProcessorErrorListener errorListener = (VoiceProcessorException error) {
    // handle error
}

_voiceProcessor?.addFrameListener(frameListener);
_voiceProcessor?.addErrorListener(errorListener);

Ask for audio record permission and start recording with the desired frame length and audio sample rate:

final int frameLength = 512;
final int sampleRate = 16000;
if (await _voiceProcessor?.hasRecordAudioPermission() ?? false) {
    try {
        await _voiceProcessor?.start(frameLength, sampleRate);
    } on PlatformException catch (ex) {
        // handle start error
    }
} else {
    // user did not grant permission
}

Stop audio recording and remove listeners:

try {
    await _voiceProcessor?.stop();
} on PlatformException catch (ex) {
    // handle stop error
}

Once audio capture has started successfully, any frame listeners assigned to the VoiceProcessor will start receiving audio frames with the given frameLength and sampleRate.

Capturing with Multiple Listeners

Any number of listeners can be added to and removed from the VoiceProcessor instance. However, the instance can only record audio with a single audio configuration (frameLength and sampleRate), which all listeners will receive once a call to start() has been made. To add multiple listeners:

VoiceProcessorFrameListener listener1 = (frame) { }
VoiceProcessorFrameListener listener2 = (frame) { }
List<VoiceProcessorFrameListener> listeners = [listener1, listener2];
_voiceProcessor?.addFrameListeners(listeners);

_voiceProcessor?.removeFrameListeners(listeners);
// or
_voiceProcessor?.clearFrameListeners();

Demo

For the Voice Processor Flutter SDK we have an example app that demonstrates how to use VoiceProcessor in a Flutter app.

Setup

Clone the flutter-voice-processor repository from GitHub:

git clone https://github.com/Picovoice/flutter-voice-processor.git

Usage

1. Install dependencies and setup environment:

cd example
flutter pub get

2. Connect a mobile device or launch a simulator. Then build and run the app:

flutter run

3. Toggle recording on and off with the button in the center of the screen. While recording, the VU meter on the screen will respond to the volume of incoming audio.

For more information on our Voice Processor demo for Flutter, head over to our GitHub repository.

Resources