scan frequency as proposed by serratus

src/quagga.js

@@ -296,16 +296,29 @@ function update() {
     }
 }
 
-function start() {
+function startContinuousUpdate() {
+    var next = null,
+        delay = 1000 / (_config.frequency || 60);
+
     _stopped = false;
-    ( function frame() {
+    (function frame(timestamp) {
+        next = next || timestamp;
         if (!_stopped) {
+            if (timestamp >= next) {
+                next += delay;
                 update();
-            if (_onUIThread && _config.inputStream.type === "LiveStream") {
+            }
             window.requestAnimFrame(frame);
         }
+    }(performance.now()));
+}
+
+function start() {
+    if (_onUIThread && _config.inputStream.type === "LiveStream") {
+        startContinuousUpdate();
+    } else {
+        update();
     }
-    }());
 }
 
 function initWorker(cb) {
@@ -360,7 +373,6 @@ function workerInterface(factory) {
     var imageWrapper;
 
     self.onmessage = function(e) {
-        setTimeout(function() {
         if (e.data.cmd === 'init') {
             var config = e.data.config;
             config.numOfWorkers = 0;
@@ -376,7 +388,6 @@ function workerInterface(factory) {
         } else if (e.data.cmd === 'setReaders') {
             Quagga.setReaders(e.data.readers);
         }
-        }, Quagga.getConfig().scanDelay || 0);
     };
 
     function onProcessed(result) {
@@ -518,8 +529,5 @@ export default {
     },
     ImageWrapper: ImageWrapper,
     ImageDebug: ImageDebug,
-    ResultCollector: ResultCollector,
+    ResultCollector: ResultCollector
-    getConfig: function getConfig() {
-        return _config;
-    }
 };