Worker for encoding raw PCM audio to WAV

wav-worker.js

self.onmessage = function (e) {
	var wavPCM = new WavePCM(e['data']['config']);
	wavPCM.record(e['data']['pcmArrays']);
	wavPCM.requestData();
};

var WavePCM = function (config) {
	this.sampleRate = config['sampleRate'] || 48000;
	this.bitDepth = config['bitDepth'] || 16;
	this.recordedBuffers = [];
	this.bytesPerSample = this.bitDepth / 8;
};

WavePCM.prototype.record = function (buffers) {
	this.numberOfChannels = this.numberOfChannels || buffers.length;
	var bufferLength = buffers[0].length;
	var reducedData = new Uint8Array(bufferLength * this.numberOfChannels * this.bytesPerSample);

	// Interleave
	for (var i = 0; i < bufferLength; i++) {
		for (var channel = 0; channel < this.numberOfChannels; channel++) {
			var outputIndex = (i * this.numberOfChannels + channel) * this.bytesPerSample;
			var sample = buffers[channel][i];

			// Check for clipping
			if (sample > 1) {
				sample = 1;
			} else if (sample < -1) {
				sample = -1;
			}

			// bit reduce and convert to uInt
			switch (this.bytesPerSample) {
				case 4:
					sample = sample * 2147483648;
					reducedData[outputIndex] = sample;
					reducedData[outputIndex + 1] = sample >> 8;
					reducedData[outputIndex + 2] = sample >> 16;
					reducedData[outputIndex + 3] = sample >> 24;
					break;

				case 3:
					sample = sample * 8388608;
					reducedData[outputIndex] = sample;
					reducedData[outputIndex + 1] = sample >> 8;
					reducedData[outputIndex + 2] = sample >> 16;
					break;

				case 2:
					sample = sample * 32768;
					reducedData[outputIndex] = sample;
					reducedData[outputIndex + 1] = sample >> 8;
					break;

				case 1:
					reducedData[outputIndex] = (sample + 1) * 128;
					break;

				default:
					throw 'Only 8, 16, 24 and 32 bits per sample are supported';
			}
		}
	}

	this.recordedBuffers.push(reducedData);
};

WavePCM.prototype.requestData = function () {
	var bufferLength = this.recordedBuffers[0].length;
	var dataLength = this.recordedBuffers.length * bufferLength;
	var headerLength = 44;
	var wav = new Uint8Array(headerLength + dataLength);
	var view = new DataView(wav.buffer);

	view.setUint32(0, 1380533830, false); // RIFF identifier 'RIFF'
	view.setUint32(4, 36 + dataLength, true); // file length minus RIFF identifier length and file description length
	view.setUint32(8, 1463899717, false); // RIFF type 'WAVE'
	view.setUint32(12, 1718449184, false); // format chunk identifier 'fmt '
	view.setUint32(16, 16, true); // format chunk length
	view.setUint16(20, 1, true); // sample format (raw)
	view.setUint16(22, this.numberOfChannels, true); // channel count
	view.setUint32(24, this.sampleRate, true); // sample rate
	view.setUint32(28, this.sampleRate * this.bytesPerSample * this.numberOfChannels, true); // byte rate (sample rate * block align)
	view.setUint16(32, this.bytesPerSample * this.numberOfChannels, true); // block align (channel count * bytes per sample)
	view.setUint16(34, this.bitDepth, true); // bits per sample
	view.setUint32(36, 1684108385, false); // data chunk identifier 'data'
	view.setUint32(40, dataLength, true); // data chunk length

	for (var i = 0; i < this.recordedBuffers.length; i++) {
		wav.set(this.recordedBuffers[i], i * bufferLength + headerLength);
	}

	self.postMessage(wav, [wav.buffer]);
	self.close();
};