WhisperLive/Audio-Transcription/worker.js

let recLength = 0,
    recBuffers = [],
    sampleRate,
    numChannels;

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);
            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) {
    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];
    }
    let dataview = encodeWAV(interleaved);
    let audioBlob = new Blob([dataview], {type: type});

    this.postMessage({command: 'exportWAV', data: audioBlob});
}

function getBuffer() {
    let buffers = [];
    for (let channel = 0; channel < numChannels; channel++) {
        buffers.push(mergeBuffers(recBuffers[channel], recLength));
    }
    this.postMessage({command: 'getBuffer', data: 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 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) {
    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, sampleRate, true);
    /* byte rate (sample rate * block align) */
    view.setUint32(28, sampleRate * 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;
}