add audio transcription module

Audio-Transcription/worker.js

@@ -0,0 +1,148 @@
+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;
+}