libopus.js

This is a port of libopus (1.1.2) to pure JavaScript using Emscripten for use in a browser environment.

If you do not plan to use your module in a browser-like environment, you should probably use node-opus instead which will almost certainly provide better performance at the cost of portability.

Usage

JavaScript wrappers are provided for the most common usage scenarios.

Be aware that opus is a stateful codec, therefore one and only one Encoder/Decoder should be used for one and only one stream of audio data. Packet loss also has to be signalled to the decoder.

Encoding raw PCM samples:

var Encoder = require('libopus.js').Encoder;
var enc = new Encoder({ rate: 48000, channels: 1 });
// Accepts either 16 bit signed integers (more space efficient)
var result = enc.encode(Int16Array.from([0, 256, 512, 256, 0, -256, -512));
// or 32 bit floating point numbers (used by the Web Audio API)
var result = enc.encode(Float32Array.from([0, 0.25, 0.5, 0.25]));
// result is a nodejs Buffer
someStream.write(result);

The encoder can also be used with node.js streams:

var Encoder = require('libopus.js').Encoder;
var enc = new Encoder();
// A stream can only process input in either the Int16 format or the Float32 format
var encStream = enc.stream('Int16');
// The stream can be used directly
encStream.write(Buffer.from([0, 0, 0, 1, 0, 2]));
var result = encStream.read();
// or just like any other node stream
someRawInput.pipe(encStream).pipe(someOutputStream);

Decoding compressed opus packets:

var Decoder = require('libopus.js').Decoder;
var dec = new Decoder({ rate: 48000, channels: 1 });
// Decode to Int16Array (more space efficient)
var result = dec.decodeInt16(Buffer.from(input));
// or to Float32Array (used by the Web Audio API)
var result = dec.decodeFloat32(Buffer.from(input));
// Signaling a lost packet
var result = dec.decodeInt16(null);

The decoder can also be used with node.js streams:

var Decoder = require('libopus.js').Decoder;
var dec = new Decoder();
// A stream can only produce output in either the Int16 format or the Float32 format
var decStream = dec.stream('Int16');
// The stream can be used directly
decStream.write(Buffer.from(input));
var result = encStream.read();
// or just like any other node stream
someEncodedInput.pipe(decStream).pipe(someOutputStream);
// Signaling a lost packet in a stream is done by sending an empty Buffer
encStream.write(Buffer.alloc(0));

The raw libopus module as generated by emscripten can also be accessed (this is dangerous if you do not know what you are doing):

var libopus = require('libopus.js').libopus;
var version = libopus.Pointer_stringify(libopus._opus_get_version_string());
var mem = libopus._malloc(42);
libopus._free(mem);

The Repacketizer, the Opus Multistream API, Opus Custom and some other parts have not been exported.

Building from source

Prebuilt libopus binaries are available in build/. Building these yourself is rather simple (assuming you have common build tools already installed):

1. Install Emscripten
2. Run make clean
3. Run make

License

The full license texts are available in LICENSE.md.

libopus.js itself uses the MIT license.

The Makefile has been extracted from Chris Rudmin's fork of Recorderjs which also uses the MIT license.

The native opus library is licensed under a three-clause BSD license. See the Opus Licensing page for more details. Therefore the generated libopus.js file is as well.