ogg-opus-decoder

What is ogg-opus-decoder?

The ogg-opus-decoder npm package is a JavaScript library that allows you to decode Ogg Opus audio files. It is useful for applications that need to handle audio streaming or playback in the browser or in Node.js environments.

What are ogg-opus-decoder's main functionalities?

Decoding Ogg Opus Files

This feature allows you to decode an Ogg Opus file and output the raw PCM data. The code sample demonstrates how to set up a stream to read an Ogg Opus file, decode it, and write the decoded PCM data to an output file.

const { OggOpusDecoder } = require('ogg-opus-decoder');
const fs = require('fs');

const decoder = new OggOpusDecoder();
const input = fs.createReadStream('path/to/your/file.ogg');
const output = fs.createWriteStream('path/to/output/file.pcm');

input.pipe(decoder).pipe(output);

Streaming Decoded Audio

This feature allows you to stream decoded audio directly to a speaker. The code sample demonstrates how to read an Ogg Opus file, decode it, and stream the audio to a speaker for playback.

const { OggOpusDecoder } = require('ogg-opus-decoder');
const fs = require('fs');
const Speaker = require('speaker');

const decoder = new OggOpusDecoder();
const input = fs.createReadStream('path/to/your/file.ogg');
const speaker = new Speaker({
  channels: 2,          // 2 channels (stereo)
  bitDepth: 16,         // 16-bit samples
  sampleRate: 48000     // 48,000 Hz sample rate
});

input.pipe(decoder).pipe(speaker);

Other packages similar to ogg-opus-decoder

node-opus

node-opus is a Node.js native binding to libopus, which allows for encoding and decoding of Opus audio streams. Unlike ogg-opus-decoder, node-opus provides more low-level control over the encoding and decoding process, making it suitable for applications that need to handle Opus audio streams directly.

opusscript

opusscript is a pure JavaScript implementation of the Opus codec. It can be used in both Node.js and browser environments. While it offers similar functionality to ogg-opus-decoder, it is not as performant as native bindings like node-opus or ogg-opus-decoder due to being implemented in JavaScript.

web-audio-api

web-audio-api is a high-level API for processing and synthesizing audio in web applications. It provides a wide range of audio processing capabilities, including decoding audio files. While it is more general-purpose compared to ogg-opus-decoder, it can be used to achieve similar results for decoding and playing back audio.

README

ogg-opus-decoder

ogg-opus-decoder is a Web Assembly Ogg Opus audio decoder.

• 116.0 KiB minified bundle size
• Browser and NodeJS support
• Built in Web Worker support
• Multichannel decoding (up to 8 channels)
• Based on libopusfile

See the homepage of this repository for more Web Assembly audio decoders like this one.

Checkout the demo here

Installing

• Install from NPM.

  Run npm i ogg-opus-decoder

  import { OggOpusDecoder } from 'ogg-opus-decoder';
  
  const decoder = new OggOpusDecoder();
  

• Or download the build and include it as a script.

  <script src="ogg-opus-decoder.min.js"></script>
  <script>
    const decoder = new window["ogg-opus-decoder"].OggOpusDecoder();
  </script>
  

Usage

1. Create a new instance and wait for the WASM to finish compiling. Decoding can be done on the main thread synchronously, or in a webworker asynchronously.

   Main thread synchronous decoding

   import { OggOpusDecoder } from 'ogg-opus-decoder';
   
   const decoder = new OggOpusDecoder();
   
   // wait for the WASM to be compiled
   await decoder.ready;
   

   Web Worker asynchronous decoding

   import { OggOpusDecoderWebWorker } from 'ogg-opus-decoder';
   
   const decoder = new OggOpusDecoderWebWorker();
   
   // wait for the WASM to be compiled
   await decoder.ready;
   

2. Begin decoding Ogg Opus data.

   // Decode an individual Opus frame
   const {channelData, samplesDecoded, sampleRate} = decoder.decode(oggOpusData);
   

   • NOTE: When decoding chained Ogg files (i.e. streaming) the first two Ogg packets of the next chain must be present when decoding. Errors will be returned by libopusfile if these initial Ogg packets are incomplete.

3. When done decoding, reset the decoder to decode a new stream, or free up the memory being used by the WASM module if you have no more audio to decode.

   // `reset()` clears the decoder state and allows you do decode a new stream of Ogg Opus data.
   await decoder.reset();
   
   // `free()` de-allocates the memory used by the decoder. You will need to create a new instance after calling `free()` to start decoding again.
   decoder.free();
   

API

Decoded audio is always returned in the below structure.

{
    channelData: [
      leftAudio, // Float32Array of PCM samples for the left channel
      rightAudio, // Float32Array of PCM samples for the right channel
      ... // additional channels
    ],
    samplesDecoded: 1234, // number of PCM samples that were decoded per channel
    sampleRate: 48000 // sample rate of the decoded PCM
}

Each Float32Array within channelData can be used directly in the WebAudio API for playback.

Multichannel Output

Each channel is assigned to a speaker location in a conventional surround arrangement. Specific locations depend on the number of channels, and are given below in order of the corresponding channel indices. This set of surround options and speaker location orderings is the same as those used by the Vorbis codec.

• 1 channel: monophonic (mono).
• 2 channels: stereo (left, right).
• 3 channels: linear surround (left, center, right).
• 4 channels: quadraphonic (front left, front right, rear left, rear right).
• 5 channels: 5.0 surround (front left, front center, front right, rear left, rear right).
• 6 channels: 5.1 surround (front left, front center, front right, rear left, rear right, LFE).
• 7 channels: 6.1 surround (front left, front center, front right, side left, side right, rear center, LFE).
• 8 channels: 7.1 surround (front left, front center, front right, side left, side right, rear left, rear right, LFE).

See: https://datatracker.ietf.org/doc/html/rfc7845.html#section-5.1.1.2

OggOpusDecoder

Class that decodes Ogg Opus data synchronously on the main thread.

Options

const decoder = new OggOpusDecoder({ forceStereo: true });

• forceStereo optional, defaults to false
  • Set to true to forces stereo output when decoding mono or multichannel Ogg Opus.

Getters

• decoder.ready async
  • Returns a promise that is resolved when the WASM is compiled and ready to use.

Methods

• decoder.decode(oggOpusData)
  • opusFrame Uint8Array containing Ogg Opus data.
  • Returns decoded audio.
• decoder.reset() async
  • Resets the decoder so that a new stream of Ogg Opus data can be decoded.
• decoder.free()
  • De-allocates the memory used by the decoder.
  • After calling free(), the current instance is made unusable, and a new instance will need to be created to decode additional Ogg Opus data.

OggOpusDecoderWebWorker

Class that decodes Ogg Opus data asynchronously within a web worker. Decoding is performed in a separate, non-blocking thread. Each new instance spawns a new worker allowing you to run multiple workers for concurrent decoding of multiple streams.

Options

const decoder = new OggOpusDecoderWebWorker({ forceStereo: true });

• forceStereo optional, defaults to false
  • Set to true to forces stereo output when decoding mono or multichannel Ogg Opus.

Getters

• decoder.ready async
  • Returns a promise that is resolved when the WASM is compiled and ready to use.

Methods

• decoder.decode(oggOpusData) *Async
  • opusFrame Uint8Array containing Ogg Opus data.
  • Returns a promise that resolves with the decoded audio.
• decoder.reset() async
  • Resets the decoder so that a new stream of Ogg Opus data can be decoded.
• decoder.free() async
  • De-allocates the memory used by the decoder and terminates the web worker.
  • After calling free(), the current instance is made unusable, and a new instance will need to be created to decode additional Ogg Opus data.

Properly using the Web Worker interface

OggOpusDecoderWebWorker uses async functions to send operations to the web worker without blocking the main thread. To fully take advantage of the concurrency provided by web workers, your code should avoid using await on decode operations where it will block the main thread.

Each method call on a OggOpusDecoderWebWorker instance will queue up an operation to the web worker. Operations will complete within the web worker thread one at a time and in the same order in which the methods were called.

• Good Main thread is not blocked during each decode operation. The example playAudio function is called when each decode operation completes. Also, the next decode operation can begin while playAudio is doing work on the main thread.

  const playAudio = ({ channelData, samplesDecoded, sampleRate }) => {
    // does something to play the audio data.
  }
  
  decoder.decodeFrame(data1).then(playAudio);
  decoder.decodeFrame(data2).then(playAudio);
  decoder.decodeFrame(data3).then(playAudio);
  
  // do some other operations while the audio is decoded
  

• Bad Main thread is being blocked by await during each decode operation. Synchronous code is halted while decoding completes, negating the benefits of using a webworker.

  const decoded1 = await decoder.decodeFrame(data1); // blocks the main thread
  playAudio(decoded1);
  
  const decoded2 = await decoder.decodeFrame(data2); // blocks the main thread
  playAudio(decoded2);
  
  const decoded3 = await decoder.decodeFrame(data3); // blocks the main thread
  playAudio(decoded3);
  

Examples

Decoding multiple files using a single instance of OggOpusDecoderWebWorker

This example shows how to decode multiple files using a single OggOpusDecoderWebWorker instance. This code iterates over an array of input files (Array of Uint8Arrays) and queues up each file to be decoded one at a time.

First, wait for the decoder to become ready by calling decoder.ready.

For each iteration, decode() is called, it's result is pushed to the decodedFiles array, and decoder.reset() is called to prepare the decoder for a new file. These operations are queued up to the decoder instance and will complete one after another.

Finally, a call to decoder.free() is queued to clean up the memory stored by the decoder. This resolves when it and all of the other operations before it complete.

It's important to note that there is only one await operations in this example. Decoding can happen asynchronously and you only need to await when you need to use the results of the decode operation.

  const inputFiles = [file1, file2, file3] // Array of Uint8Array file data

  const decoder = new OggOpusDecoderWebWorker();

  const decodedFiles = [];

  const decodePromise = decoder.ready // wait for the decoder to be ready
    .then(() => {
      for (const file of inputFiles) {
        decoder.decode(file) // queue the decode operation
          .then((result) => decodedFiles.push(result)); // save the decode result after decode completes
        decoder.reset(); // queue the reset operation
      }
    })
    .then(() => decoder.free()); // queue the free operation that will execute after the above operations

  // do sync operations here

  // await when you need to have the all of the audio data decoded
  await decodePromise;

Decoding multiple files using multiple instances of OggOpusDecoderWebWorker

This example shows how to decode multiple files using multiple instances of OggOpusDecoderWebWorker. This code iterates over an array of input files (Array of Uint8Arrays) and spawns a new OggOpusDecoderWebWorker instance for each file and decodes the file. If you want to take full advantage of multi-core devices, this is the approach you will want to take since it will parallelize the decoding

For each input file, a new decoder is created, and the file is decoded using the decode() after decoder.ready is resolved. The result of the decode() operation is returned, and a finally() function on the promise calls decoder.free() to free up the instance after the decode operations are completed.

Finally, Promise.all() wraps this array of promises and resolves when all decode operations are complete.

It's important to note that there is only one await operation in this example. Decoding can happen asynchronously and you only need to await when you need to use the results of the decode operation.

  const inputFiles = [file1, file2, file3] // Array of Uint8Array file data

  // loops through each Uint8Array in `inputFiles` and decodes the files in separate threads
  const decodePromise = Promise.all(
    inputFiles.map((file) => {
      const decoder = new OggOpusDecoderWebWorker();

      return decoder.ready
        .then(() => decoder.decode(file)) // decode the input file
        .finally(() => decoder.free()); // free the decoder after resolving the decode result
    })
  );

  // do sync operations here

  // await when you need to have the all of the audio data decoded
  const decodedFiles = await decodePromise;