add audio transcription module

Audio-Transcription/workers/Mp3Worker.js

@@ -0,0 +1,106 @@
+importScripts("/../encoders/Mp3Encoder.min.js");
+
+let NUM_CH = 2, // constant
+    sampleRate = 16000,
+    options = undefined,
+    maxBuffers = undefined,
+    encoder = undefined,
+    recBuffers = undefined,
+    socket = undefined,
+    bufferCount = 0;
+
+function error(message) {
+  self.postMessage({ command: "error", message: "mp3: " + message });
+}
+
+function init(data) {
+  if (data.config.numChannels === NUM_CH) {
+    sampleRate = data.config.sampleRate;
+    options = data.options;
+  } else
+    error("numChannels must be " + NUM_CH);
+};
+
+function setOptions(opt) {
+  if (encoder || recBuffers)
+    error("cannot set options during recording");
+  else
+    options = opt;
+}
+
+function start(bufferSize) {
+  maxBuffers = Math.ceil(options.timeLimit * sampleRate / bufferSize);
+  // TODO: get server address from user
+  socket = new WebSocket("ws://localhost:9090/");
+  socket.onopen = function(e) { 
+    socket.send("handshake");
+  };
+  socket.onmessage = (event) => {
+    console.log(event.data);
+  };
+
+  if (options.encodeAfterRecord)
+    recBuffers = [];
+  else
+    encoder = new Mp3LameEncoder(sampleRate, options.mp3.bitRate);
+}
+
+function record(buffer) {
+  if (bufferCount++ < maxBuffers){
+    if (encoder)
+      encoder.encode(buffer);
+    else 
+      recBuffers.push(buffer);
+    
+    // send buffer to server
+    socket.send(buffer[0]);
+  }
+  else
+    self.postMessage({ command: "timeout" });
+};
+
+function postProgress(progress) {
+  self.postMessage({ command: "progress", progress: progress });
+};
+
+function finish() {
+  if (recBuffers) {
+    postProgress(0);
+    encoder = new Mp3LameEncoder(sampleRate, options.mp3.bitRate);
+    let timeout = Date.now() + options.progressInterval;
+    while (recBuffers.length > 0) {
+      encoder.encode(recBuffers.shift());
+      let now = Date.now();
+      if (now > timeout) {
+        postProgress((bufferCount - recBuffers.length) / bufferCount);
+        timeout = now + options.progressInterval;
+      }
+    }
+    postProgress(1);
+  }
+  self.postMessage({
+    command: "complete",
+    blob: encoder.finish(options.mp3.mimeType)
+  });
+  cleanup();
+};
+
+function cleanup() {
+  encoder = recBuffers = undefined;
+  bufferCount = 0;
+  socket.close();
+}
+
+self.onmessage = function(event) {
+  let data = event.data;
+  switch (data.command) {
+    case "init":    init(data);                 break;
+    case "options": setOptions(data.options);   break;
+    case "start":   start(data.bufferSize);     break;
+    case "record":  record(data.buffer);        break;
+    case "finish":  finish();                   break;
+    case "cancel":  cleanup();
+  }
+};
+
+self.postMessage({ command: "loaded" });