libcelt7.js

This is a port of CELT (0.7.1) 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-celt 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 CELT 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('libcelt7.js').Encoder;
var enc = new Encoder({ rate: 48000, frameSize: 256, channels: 1 });
// Accepts either 16 bit signed integers (more space efficient)
var result = enc.encode(Int16Array.from([0, 256, 512, 256, 0, -256, -512, ..]), 960);
// 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, ..]), 960);
// in either case, exactly frameSize samples have to be passed in per channel
// The second parameter is the target size of the encoded packet (max size with VBR).
// result is a nodejs Buffer
someStream.write(result);

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

var Encoder = require('libcelt7.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', 960);
// 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('libcelt7.js').Decoder;
var dec = new Decoder({ rate: 48000, frameSize: 256, 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('libcelt7.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 libcelt module as generated by emscripten can also be accessed (this is dangerous if you do not know what you are doing):

var libcelt = require('libcelt7.js').libcelt;
var version = libcelt.Pointer_stringify(libcelt._opus_get_version_string());
var mem = libcelt._malloc(42);
libopus._free(mem);

Building from source

Prebuilt libcelt 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.

libcelt7.js itself uses the MIT license.

The native CELT library is licensed under a three-clause BSD license. See the CELT COPYING file for more details. Therefore the generated libcelt7.js file is as well.