@tilawi/expo-pcm-recorder

A minimal Expo module that streams raw microphone audio to JavaScript as mono float32 PCM at the sample rate you ask for (e.g. 16 kHz), in fixed-size chunks. Built for on-device speech recognition, where you want samples rather than an encoded file.

It powers voice search and memorization checks in the Tilawi Quran app, together with @tilawi/react-native-quran-asr.

• iOS: AVAudioEngine input tap, converted with AVAudioConverter. The audio session is set to .playAndRecord (Bluetooth allowed, mixes with and ducks other audio) and restored to its previous category when recording stops.
• Android: AudioRecord from the MIC source, 16-bit PCM scaled to [-1, 1], with transient audio focus while recording.
• Safe to import in a build that doesn't include the native code: isPcmRecorderAvailable is then false and nothing crashes.

Install

npx expo install @tilawi/expo-pcm-recorder

Then rebuild your development client (this module has native code; it doesn't work in Expo Go).

Microphone permission. This module doesn't request permission itself. Declare it and ask for it with another module that owns the same OS permission, for example expo-audio:

{ "plugins": [["expo-audio", { "microphonePermission": "Allow $(PRODUCT_NAME) to hear your recitation." }]] }

import { requestRecordingPermissionsAsync } from 'expo-audio';
await requestRecordingPermissionsAsync();

Usage

import {
  addPcmChunkListener,
  isPcmRecorderAvailable,
  startPcmRecording,
  stopPcmRecording,
} from '@tilawi/expo-pcm-recorder';

const chunks: number[][] = [];
const sub = addPcmChunkListener((samples) => chunks.push(samples)); // float32 in [-1, 1]

await startPcmRecording(16000, 100); // 16 kHz, one chunk every 100 ms
// ... later
await stopPcmRecording(); // remaining audio is delivered before this resolves
sub?.remove();

| API | | |---|---| | startPcmRecording(sampleRate, intervalMs) | Start capturing. Rejects if the permission is missing, the microphone is busy, or a recording is already running. | | stopPcmRecording() | Stop and flush the remaining audio. Safe to call when idle. | | addPcmChunkListener(fn) | Receive number[] chunks of mono samples. Returns a subscription (null when unavailable). | | isPcmRecorderAvailable | false when the native module isn't in the running binary. |

Android caveat: if the capture thread doesn't finish within 1 s of stopping (not observed in practice), a final chunk may arrive after stopPcmRecording() resolves.

Credits

Inspired by @siteed/audio-studio (MIT) by @deeeed; the native sources note which of its capture settings this module mirrors.

License

MIT