Decoding

You can decode audio data independently, without creating an AudioContext, using the exported functions decodeAudioData and decodePCMInBase64.

If you already have an audio context, you can decode audio data directly using its decodeAudioData function; the decoded audio will then be automatically resampled to match the context's sampleRate.

caution

Supported file formats:

• aac
• flac
• m4a
• mp3
• mp4
• ogg
• opus
• wav

decodeAudioData

Decodes audio data from either a file path or an ArrayBuffer. The optional sampleRate parameter lets you resample the decoded audio; if not provided, the original sample rate from the file is used.

Parameter	Type	Description
input	ArrayBuffer	ArrayBuffer with audio data.
	string	Path to audio file located on the device.
sampleRate Optional	number	Target sample rate for the decoded audio.

Returns Promise<AudioBuffer>.

Example decoding with memory block

const url = ... // url to an audio

  const buffer = await fetch(url)
    .then((response) => response.arrayBuffer())
    // resample decoded audio to 48000 Hz
    .then((arrayBuffer) => decodeAudioData(arrayBuffer, 48000))
    .catch((error) => {
      console.error('Error decoding audio data source:', error);
      return null;
    });

Example using expo-asset library

import { Asset } from 'expo-asset';

const buffer = await Asset.fromModule(require('@/assets/music/example.mp3'))
    .downloadAsync()
    .then((asset) =>  {
      if (!asset.localUri) {
        throw new Error('Failed to load audio asset');
      }
      // sampleRate not provided, so file will be decoded in original sampleRate
      return decodeAudioData(asset.localUri);
    })

decodePCMInBase64

Decodes base64-encoded PCM audio data.

Parameter	Type	Description
base64String	string	Base64-encoded PCM audio data.
inputSampleRate	number	Sample rate of the input PCM data.
inputChannelCount	number	Number of channels in the input PCM data.
isInterleaved Optional	boolean	Whether the PCM data is interleaved. Default is true.

Returns Promise<AudioBuffer>

Example decoding with data in base64 format

const data = ... // data encoded in base64 string
// data is interleaved (Channel1, Channel2, Channel1, Channel2, ...)
const buffer = await decodeAudioData(data, 4800, 2, true);