The Expo Play Audio Stream module is a powerful tool for recording and streaming audio data in your Expo-based React Native applications. It provides a seamless way to record audio from the microphone and play audio chunks in real-time, allowing you to build audio-centric features like voice assistants, audio players, voice recorders, and more.
Expo's built-in audio capabilities are limited to playing pre-loaded audio files and basic recording. The Expo Audio Stream module was created to address these limitations, enabling developers to record high-quality audio with real-time streaming capabilities and have more control over both the recording and playback process. The module provides features like dual-stream output (original and 16kHz versions) which is particularly useful for voice activity detection and speech recognition applications.
Here's how you can use the Expo Play Audio Stream module for different scenarios:
import { ExpoPlayAudioStream, EncodingTypes, PlaybackModes } from 'expo-audio-stream';
// Example of standard recording and playback with specific encoding
async function handleStandardRecording() {
try {
// Configure sound playback settings
await ExpoPlayAudioStream.setSoundConfig({
sampleRate: 44100,
playbackMode: PlaybackModes.REGULAR
});
// Start recording with configuration
const { recordingResult, subscription } = await ExpoPlayAudioStream.startRecording({
sampleRate: 48000,
channels: 1,
encoding: 'pcm_16bit',
interval: 250, // milliseconds
onAudioStream: (event) => {
console.log('Received audio stream:', {
audioDataBase64: event.data,
position: event.position,
eventDataSize: event.eventDataSize,
totalSize: event.totalSize,
soundLevel: event.soundLevel // New property for audio level monitoring
});
}
});
// After some time, stop recording
setTimeout(async () => {
const recording = await ExpoPlayAudioStream.stopRecording();
console.log('Recording stopped:', recording);
// Play the recorded audio with specific encoding format
const turnId = 'example-turn-1';
await ExpoPlayAudioStream.playAudio(base64Content, turnId, EncodingTypes.PCM_S16LE);
// Clean up
subscription?.remove();
}, 5000);
} catch (error) {
console.error('Audio handling error:', error);
}
}
// You can also subscribe to audio events from anywhere
const audioSubscription = ExpoPlayAudioStream.subscribeToAudioEvents(async (event) => {
console.log('Audio event received:', {
data: event.data,
soundLevel: event.soundLevel // Sound level can be used for visualization or voice detection
});
});
// Don't forget to clean up when done
// audioSubscription.remove();These methods are designed for scenarios where you need to record and play audio at the same time:
import { ExpoPlayAudioStream, EncodingTypes, PlaybackModes } from 'expo-audio-stream';
// Example of simultaneous recording and playback with voice processing
async function handleSimultaneousRecordAndPlay() {
try {
// Configure sound playback with optimized voice processing settings
await ExpoPlayAudioStream.setSoundConfig({
sampleRate: 44100,
playbackMode: PlaybackModes.VOICE_PROCESSING
});
// Start microphone with voice processing
const { recordingResult, subscription } = await ExpoPlayAudioStream.startMicrophone({
enableProcessing: true,
onAudioStream: (event) => {
console.log('Received audio stream with voice processing:', {
audioDataBase64: event.data,
soundLevel: event.soundLevel
});
}
});
// Play audio while recording is active, with specific encoding format
const turnId = 'response-turn-1';
await ExpoPlayAudioStream.playSound(someAudioBase64, turnId, EncodingTypes.PCM_F32LE);
// Play a complete WAV file directly
await ExpoPlayAudioStream.playWav(wavBase64Data);
// Example of controlling playback during recording
setTimeout(async () => {
// Clear the queue for a specific turn
await ExpoPlayAudioStream.clearSoundQueueByTurnId(turnId);
// Interrupt current playback
await ExpoPlayAudioStream.interruptSound();
// Resume playback
await ExpoPlayAudioStream.resumeSound();
// Stop microphone recording
await ExpoPlayAudioStream.stopMicrophone();
// Clean up
subscription?.remove();
}, 5000);
} catch (error) {
console.error('Simultaneous audio handling error:', error);
}
}The Expo Play Audio Stream module provides the following methods:
-
destroy(): Destroys the audio stream module, cleaning up all resources. This should be called when the module is no longer needed. It will reset all internal state and release audio resources. -
startRecording(recordingConfig: RecordingConfig): Starts microphone recording with the specified configuration. Returns a promise with recording result and audio event subscription. Throws an error if the recording fails to start. -
stopRecording(): Stops the current microphone recording. Returns a promise that resolves to the audio recording data. Throws an error if the recording fails to stop. -
playAudio(base64Chunk: string, turnId: string, encoding?: Encoding): Plays a base64 encoded audio chunk with the specified turn ID. The optional encoding parameter allows specifying the format of the audio data ('pcm_f32le' or 'pcm_s16le', defaults to 'pcm_s16le'). Throws an error if the audio chunk fails to stream. -
pauseAudio(): Pauses the current audio playback. Throws an error if the audio playback fails to pause. -
stopAudio(): Stops the currently playing audio. Throws an error if the audio fails to stop. -
clearPlaybackQueueByTurnId(turnId: string): Clears the playback queue for a specific turn ID. Throws an error if the playback queue fails to clear. -
setSoundConfig(config: SoundConfig): Sets the sound player configuration with options for sample rate and playback mode. The SoundConfig interface accepts:sampleRate: The sample rate for audio playback in Hz (16000, 44100, or 48000)playbackMode: The playback mode ('regular', 'voiceProcessing', or 'conversation')useDefault: When true, resets to default configuration regardless of other parameters
Default settings are:
- Android: sampleRate: 44100, playbackMode: 'regular'
- iOS: sampleRate: 44100.0, playbackMode: 'regular'
These methods are specifically designed for scenarios where you need to record and play audio at the same time:
-
startMicrophone(recordingConfig: RecordingConfig): Starts microphone streaming with voice processing enabled. Returns a promise that resolves to an object containing the recording result and a subscription to audio events. Throws an error if the recording fails to start. -
stopMicrophone(): Stops the current microphone streaming. Returns a promise that resolves to the audio recording data or null. Throws an error if the microphone streaming fails to stop. -
playSound(audio: string, turnId: string, encoding?: Encoding): Plays a sound while recording is active. Uses voice processing to prevent feedback. The optional encoding parameter allows specifying the format of the audio data ('pcm_f32le' or 'pcm_s16le', defaults to 'pcm_s16le'). Throws an error if the sound fails to play. -
stopSound(): Stops the currently playing sound in simultaneous mode. Throws an error if the sound fails to stop. -
interruptSound(): Interrupts the current sound playback in simultaneous mode. Throws an error if the sound fails to interrupt. -
resumeSound(): Resumes the current sound playback in simultaneous mode. Throws an error if the sound fails to resume. -
clearSoundQueueByTurnId(turnId: string): Clears the sound queue for a specific turn ID in simultaneous mode. Throws an error if the sound queue fails to clear. -
playWav(wavBase64: string): Plays a WAV format audio file from base64 encoded data. Unlike playSound(), this method plays the audio directly without queueing. The audio data should be base64 encoded WAV format. Throws an error if the WAV audio fails to play. -
toggleSilence(): Toggles the silence state of the microphone during recording. This can be useful for temporarily muting the microphone without stopping the recording session. Throws an error if the microphone fails to toggle silence. -
promptMicrophoneModes(): Prompts the user to select the microphone mode (iOS specific feature).
-
subscribeToAudioEvents(onMicrophoneStream: (event: AudioDataEvent) => Promise<void>): Subscribes to audio events emitted during recording/streaming. The callback receives an AudioDataEvent containing:data: Base64 encoded audio data at original sample rateposition: Current position in the audio streamfileUri: URI of the recording fileeventDataSize: Size of the current audio data chunktotalSize: Total size of recorded audio so farsoundLevel: Optional sound level measurement that can be used for visualization Returns a subscription that should be cleaned up when no longer needed.
-
subscribeToSoundChunkPlayed(onSoundChunkPlayed: (event: SoundChunkPlayedEventPayload) => Promise<void>): Subscribes to events emitted when a sound chunk has finished playing. The callback receives a payload indicating if this was the final chunk. Returns a subscription that should be cleaned up when no longer needed. -
subscribe<T>(eventName: string, onEvent: (event: T | undefined) => Promise<void>): Generic subscription method for any event emitted by the module. Available events include:AudioData: Emitted when new audio data is available during recordingSoundChunkPlayed: Emitted when a sound chunk finishes playingSoundStarted: Emitted when sound playback begins
Note: When playing audio, you can use the special turnId "supspend-sound-events" to suppress sound events for that particular playback. This is useful when you want to play audio without triggering the sound events.
Encoding: Defines the audio encoding format, either 'pcm_f32le' (32-bit float) or 'pcm_s16le' (16-bit signed integer)EncodingTypes: Constants for audio encoding formats (EncodingTypes.PCM_F32LE, EncodingTypes.PCM_S16LE)PlaybackMode: Defines different playback modes ('regular', 'voiceProcessing', or 'conversation')PlaybackModes: Constants for playback modes (PlaybackModes.REGULAR, PlaybackModes.VOICE_PROCESSING, PlaybackModes.CONVERSATION)SampleRate: Supported sample rates (16000, 44100, or 48000 Hz)RecordingEncodingType: Encoding type for recording ('pcm_32bit', 'pcm_16bit', or 'pcm_8bit')
All methods are static and most return Promises that resolve when the operation is complete. Error handling is built into each method, with descriptive error messages if operations fail.
The Swift implementation of the Expo Audio Stream module uses the AVFoundation framework to handle audio playback. It utilizes a dual-buffer queue system to ensure smooth and uninterrupted audio streaming. The module also configures the audio session and manages the audio engine and player node.
The Kotlin implementation of the Expo Audio Stream module uses the AudioTrack class from the Android framework to handle audio playback. It uses a concurrent queue to manage the audio chunks and a coroutine-based playback loop to ensure efficient and asynchronous processing of the audio data.
The module implements several audio optimizations for voice recording:
- On iOS 15 and later, users are prompted with system voice isolation options (
microphoneModes), allowing them to choose their preferred voice isolation level. - When simultaneous recording and playback is enabled, the module uses iOS voice processing which includes:
- Noise reduction
- Echo cancellation
- Voice optimization
Note: Voice processing may result in lower audio levels as it optimizes for voice clarity over volume. This is a trade-off made to ensure better voice quality and reduce background noise.
- The Expo Play Audio Stream module is designed to work with specific audio formats (RIFF, 16 kHz, 16-bit, mono PCM). If your audio data is in a different format, you may need to convert it before using the module.
- The module does not provide advanced features like audio effects or mixing. It is primarily focused on real-time audio streaming and recording.
- The performance of the module may depend on the device's hardware capabilities and the complexity of the audio data being streamed.
Contributions to the Expo Audio Stream module are welcome! If you encounter any issues or have ideas for improvements, feel free to open an issue or submit a pull request on the GitHub repository.
The Expo Play Audio Stream module is licensed under the MIT License.