wasm-media-encoders

The LAME MP3 and Ogg Vorbis audio encoders, compiled to minimal WebAssembly and ready for use in the browser or Node.

Why?

While some browsers have native encoding using the MediaRecorder API, it only supports a small number of codecs.

This package aims to fill the gap by compiling the reference LAME and Ogg Vorbis encoders to WebAssembly. The resulting package is tiny and fast:

_{*When using ESNext syntax and no polyfills}

Installation

yarn add wasm-media-encoders

or

npm install wasm-media-encoders

Getting started

With webpack or .mjs file in Node 12+:

import { createMp3Enoder, createOggEncoder } from "wasm-media-encoders";

createOggEncoder().then((encoder) => {
  /* Configure and use the encoder */
});
createMp3Encoder().then((encoder) => {
  /* Configure and use the encoder */
});

With a <script> tag:

<script src="https://unpkg.com/wasm-media-encoders/dist/umd/WasmMediaEncoder.min.js"></script>
<script>
  // The UMD package will fetch() the WASM binaries from
  // unpkg.com by default to reduce size

  WasmMediaEncoder.createMp3Encoder().then((encoder) => {
    /* Configure and use the encoder */
  });
</script>

Using CommonJS in Node:

const { createMp3Encoder } = require("wasm-media-encoders");
createMp3Encoder().then((encoder) => {
  /* Configure and use the encoder */
});

If you'd like to use ESNext syntax and transpile yourself, use the wasm-media-encoders/esnext path.

Example usage

createMp3Encoder().then((encoder) => {
  encoder.configure({
    sampleRate: 48000,
    channels: 2,
    vbrQuality: 2,
  });

  let outBuffer = new Uint8Array(1024 * 1024);
  let offset = 0;
  let moreData = true;

  while (true) {
    const mp3Data = moreData
      ? encoder.encode([
          pcm_l /* Float32Array of left channel PCM data */,
          pcm_r /* Float32Array of right channel PCM data */,
        ])
      : /* finalize() returns the last few frames */
        encoder.finalize();

    /* mp3Data is a Uint8Array that is still owned by the encoder and MUST be copied */

    if (mp3Data.length + offset > outBuffer.length) {
      const newBuffer = new Uint8Array(mp3Data.length + offset);
      newBuffer.set(outBuffer);
      outBuffer = newBuffer;
    }

    outBuffer.set(mp3Data, offset);
    offset += mp3Data.length;

    if (!moreData) {
      break;
    }

    moreData = false;
  }

  return new Uint8Array(outBuffer.buffer, 0, offset);

  /* Or encoder can be reused without calling createEncoder() again:

  encoder.configure({...new params})
  encoder.encode()
  encoder.finalize() */
});

Reducing bundle size

By default, this package inlines the WASM binary as a base64-encoded data URL. This make importing the encoder easy, but also increases the bundle size by about 30%. With webpack, you can load the WASM directly (found in wasm-media-encoders/wasm/(mp3|ogg).wasm), passing the URL as the second parameter to createEncoder().

Webpack v4

Besides using file-loader, you also need to disable WASM parsing in the webpack config:

import { createEncoder } from "wasm-media-encoders";
import wasm from "file-loader!wasm-media-encoders/wasm/mp3.wasm";

createEncoder("audio/mpeg", wasm).then((encoder) => {
  /* Now mp3.wasm will be copied to output dir by webpack and fetch()ed at runtime */
});

// webpack.config.js

module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.wasm$/,
        type: "javascript/auto",
      },
    ],
  },
};

Webpack v5

Using asset modules and URL assets is easy in webpack v5:

import { createEncoder } from "wasm-media-encoders";

createEncoder(
  "audio/mpeg",
  new URL("wasm-media-encoder/wasm/mp3", import.meta.url)
).then((encoder) => {
  /* Now mp3.wasm will be copied to output dir by webpack and fetch()ed at runtime */
});

API

Named exports:

createMp3Encoder(): Promise<WasmMediaEncoder>

createOggEncoder(): Promise<WasmMediaEncoder>

These two named exports use inline base-64 encoded WASM binaries (or fetch() from unpkg.com in the case of UMD). Tree-shaking in bundlers should prevent unused encoders from being included in the final bundle.

createEncoder(mimeType, wasm, moduleCallback?): Promise<WasmMediaEncoder>

jsLibraryVersion(): string

Returns an opaque version string for the Javascript portion of this library. This string must match the WASM version string provided in the moduleCallback wasmVersion parameter documented above.

WasmMediaEncoder

configure(options): void

Configures the encoder. This method can be called at any time to reset the state of the encoder, including after finalize().

The options object is a union of common properties and encoder-specific ones. All common options are required.

Options for MIME type audio/mpeg (MP3):

Options for MIME type audio/ogg (Ogg Vorbis):

encode(samples): Uint8Array

finalize(): Uint8Array

Flushes the encoder and returns the last few encoded samples. May return a Uint8Array of length zero. The returned Uint8Array is owned by the encoder and MUST be copied before any other encoder methods are called.

Building

Dev Container

The easiest way to get started is by creating a development container using the included .devcontainer/devcontainer.json. Tools that support dev containers can be found here. Development containers require a Docker or Podman installation. Full instructions for Visual Studio Code can be found here.

Manually setting up environment

To manually set up a development environment, you must install the following prerequisites:

1. Emscripten SDK (v2.0.8)

2. Node 20

Note that the Emscripten SDK includes Node 12 and will include it in the PATH. Node 20 must appear before Node 12 in the PATH.

Enable yarn using corepack:

corepack enable
# If no network access, install the checked-in version:
# corepack install -g .devcontainer/corepack.tgz

Building

To create a release build:

make

Testing

make test

License

This project is licensed under the terms of the MIT license.