Skip to content

Instantly share code, notes, and snippets.

Embed
What would you like to do?
recorderWorker.js with bitrate decreasing
export default function inlineWorker() {
let recLength = 0,
recBuffers = [],
sampleRate,
numChannels;
this.onmessage = function(e){
switch(e.data.command){
case 'init':
init(e.data.config);
break;
case 'record':
record(e.data.buffer);
break;
case 'exportWAV':
exportWAV(e.data.type, e.data.rate);
break;
case 'getBuffer':
getBuffer();
break;
case 'clear':
clear();
break;
}
};
function init(config) {
sampleRate = config.sampleRate;
numChannels = config.numChannels;
initBuffers();
}
function record(inputBuffer) {
for (var channel = 0; channel < numChannels; channel++) {
recBuffers[channel].push(inputBuffer[channel]);
}
recLength += inputBuffer[0].length;
}
function exportWAV(type, rate) {
rate = rate || sampleRate;
let buffers = [];
for (let channel = 0; channel < numChannels; channel++) {
buffers.push(mergeBuffers(recBuffers[channel], recLength));
}
let interleaved;
if (numChannels === 2) {
interleaved = interleave(buffers[0], buffers[1]);
} else {
interleaved = buffers[0];
}
var downsampledBuffer = downsampleBuffer(interleaved, rate);
let dataview = encodeWAV(downsampledBuffer, rate);
let audioBlob = new Blob([dataview], {type: type});
this.postMessage(audioBlob);
}
function getBuffer() {
let buffers = [];
for (let channel = 0; channel < numChannels; channel++) {
buffers.push(mergeBuffers(recBuffers[channel], recLength));
}
this.postMessage(buffers);
}
function clear() {
recLength = 0;
recBuffers = [];
initBuffers();
}
function initBuffers() {
for (let channel = 0; channel < numChannels; channel++) {
recBuffers[channel] = [];
}
}
function mergeBuffers(recBuffers, recLength) {
let result = new Float32Array(recLength);
let offset = 0;
for (let i = 0; i < recBuffers.length; i++) {
result.set(recBuffers[i], offset);
offset += recBuffers[i].length;
}
return result;
}
function interleave(inputL, inputR) {
let length = inputL.length + inputR.length;
let result = new Float32Array(length);
let index = 0,
inputIndex = 0;
while (index < length) {
result[index++] = inputL[inputIndex];
result[index++] = inputR[inputIndex];
inputIndex++;
}
return result;
}
function downsampleBuffer(buffer, rate) {
if (rate == sampleRate) {
return buffer;
}
if (rate > sampleRate) {
throw "downsampling rate show be smaller than original sample rate";
}
var sampleRateRatio = sampleRate / rate;
var newLength = Math.round(buffer.length / sampleRateRatio);
var result = new Float32Array(newLength);
var offsetResult = 0;
var offsetBuffer = 0;
while (offsetResult < result.length) {
var nextOffsetBuffer = Math.round((offsetResult + 1) * sampleRateRatio);
var accum = 0, count = 0;
for (var i = offsetBuffer; i < nextOffsetBuffer && i < buffer.length; i++) {
accum += buffer[i];
count++;
}
result[offsetResult] = accum / count;
offsetResult++;
offsetBuffer = nextOffsetBuffer;
}
return result;
}
function floatTo16BitPCM(output, offset, input) {
for (let i = 0; i < input.length; i++, offset += 2) {
let s = Math.max(-1, Math.min(1, input[i]));
output.setInt16(offset, s < 0 ? s * 0x8000 : s * 0x7FFF, true);
}
}
function writeString(view, offset, string) {
for (let i = 0; i < string.length; i++) {
view.setUint8(offset + i, string.charCodeAt(i));
}
}
function encodeWAV(samples, rate) {
let buffer = new ArrayBuffer(44 + samples.length * 2);
let view = new DataView(buffer);
/* RIFF identifier */
writeString(view, 0, 'RIFF');
/* RIFF chunk length */
view.setUint32(4, 36 + samples.length * 2, true);
/* RIFF type */
writeString(view, 8, 'WAVE');
/* format chunk identifier */
writeString(view, 12, 'fmt ');
/* format chunk length */
view.setUint32(16, 16, true);
/* sample format (raw) */
view.setUint16(20, 1, true);
/* channel count */
view.setUint16(22, numChannels, true);
/* sample rate */
view.setUint32(24, rate, true);
/* byte rate (sample rate * block align) */
view.setUint32(28, rate * 4, true);
/* block align (channel count * bytes per sample) */
view.setUint16(32, numChannels * 2, true);
/* bits per sample */
view.setUint16(34, 16, true);
/* data chunk identifier */
writeString(view, 36, 'data');
/* data chunk length */
view.setUint32(40, samples.length * 2, true);
floatTo16BitPCM(view, 44, samples);
return view;
}
}
@itsmepetrov

This comment has been minimized.

Copy link
Owner Author

itsmepetrov commented Sep 9, 2016

Test for 5 seconds record

Rate Channels Size
44100 2 868396
16000 2 332926
8000 2 166484
44100 1 499756
16000 1 184318
8000 1 90694
Sign up for free to join this conversation on GitHub. Already have an account? Sign in to comment
You can’t perform that action at this time.