Rewriting the SoundMeter class to be RMS and be encapsulated differently

This CL changes the SoundMeter to be root-mean-square.
It also changes the interface between the meter and the display to be based on the display calling down to the meter rather than the meter calling up to the display.

A graphic display of the results is also added.

BUG=
R=cwilso@google.com, dutton@google.com, henrika@webrtc.org, juberti@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/5439004

git-svn-id: http://webrtc.googlecode.com/svn/trunk@5256 4adac7df-926f-26a2-2b94-8c16560cd09d

samples/js/base/adapter.js

@@ -77,13 +77,17 @@ if (navigator.mozGetUserMedia) {
   };
 
   // Fake get{Video,Audio}Tracks
-  MediaStream.prototype.getVideoTracks = function() {
-    return [];
-  };
+  if (!MediaStream.prototype.getVideoTracks) {
+    MediaStream.prototype.getVideoTracks = function() {
+      return [];
+    };
+  }
 
-  MediaStream.prototype.getAudioTracks = function() {
-    return [];
-  };
+  if (!MediaStream.prototype.getAudioTracks) {
+    MediaStream.prototype.getAudioTracks = function() {
+      return [];
+    };
+  }
 } else if (navigator.webkitGetUserMedia) {
   console.log("This appears to be Chrome");
 

samples/js/demos/html/local-audio-volume.html

@@ -9,7 +9,52 @@
   var buttonStart;
   var buttonStop;
   var localStream;
-  var soundMeter;
+  var reporter;
+  var audioContext;
+
+  // Meter class that generates a number correlated to audio volume.
+  // The meter class itself displays nothing, but it makes the
+  // instantaneous and time-decaying volumes available for inspection.
+  // It also reports on the fraction of samples that were at or near
+  // the top of the measurement range.
+  function SoundMeter(context) {
+    this.context = context
+    this.volume = 0.0;
+    this.slow_volume = 0.0;
+    this.clip = 0.0;
+    this.script = context.createScriptProcessor(2048, 1, 1);
+    that = this;
+    this.script.onaudioprocess = function(event) {
+      var input = event.inputBuffer.getChannelData(0);
+      var i;
+      var sum = 0.0;
+      var clipcount = 0;
+      for (i = 0; i < input.length; ++i) {
+        sum += input[i] * input[i];
+        if (Math.abs(input[i]) > 0.99) {
+          clipcount += 1
+        }
+      }
+      that.volume = Math.sqrt(sum / input.length);
+      that.slow_volume = 0.95 * that.slow_volume + 0.05 * that.volume;
+      that.clip = clipcount / input.length;
+    }
+  }
+
+  SoundMeter.prototype.connectToSource = function(stream) {
+    console.log('SoundMeter connecting');
+    this.mic = this.context.createMediaStreamSource(stream);
+    this.mic.connect(this.script);
+    // Necessary to make sample run, but should not be.
+    this.script.connect(this.context.destination);
+  }
+
+  SoundMeter.prototype.stop = function() {
+    this.mic.disconnect();
+    this.script.disconnect();
+  }
+
+  // End of SoundMeter class.
 
   $ = function(id) {
     return document.getElementById(id);
@@ -26,11 +71,13 @@
     buttonStart.enabled = true;
     buttonStop.enabled = false;
     localStream.stop();
+    clearInterval(reporter);
+    soundMeter.stop();
   }
 
   function gotStream(stream) {
-    videoTracks = stream.getVideoTracks();
-    audioTracks = stream.getAudioTracks();
+    var videoTracks = stream.getVideoTracks();
+    var audioTracks = stream.getAudioTracks();
     if (audioTracks.length == 1 && videoTracks.length == 0) {
       console.log('gotStream({audio:true, video:false})');
       console.log('Using audio device: ' + audioTracks[0].label);
@@ -42,18 +89,25 @@
       };
 
       localStream = stream;
-      soundMeter = new SoundMeter()
-      meter = $('volume');
-      decaying_meter = $('decaying_volume');
-      decaying_volume = 0.0;
-      soundMeter.showVolume = function(volume) {
-         meter.innerHTML = volume.toFixed(2);
-         decaying_volume = volume * 0.05 + decaying_volume * 0.95;
-         decaying_meter.innerHTML = decaying_volume.toFixed(2);
-      }
-      soundMeter.connect(stream)
+      var soundMeter = new SoundMeter(audioContext);
+      soundMeter.connectToSource(stream);
+
+      // Set up reporting of the volume every 0.2 seconds.
+      var meter = $('volume');
+      var decaying_meter = $('decaying_volume');
+      var meter_canvas = $('graphic_volume').getContext('2d');
+      var meter_slow = $('graphic_slow').getContext('2d');
+      var meter_clip = $('graphic_clip').getContext('2d');
+      reporter = setInterval(function() {
+         meter.textContent = soundMeter.volume.toFixed(2);
+         decaying_meter.textContent = soundMeter.slow_volume.toFixed(2);
+         paintMeter(meter_canvas, soundMeter.volume);
+         paintMeter(meter_slow, soundMeter.slow_volume);
+         paintMeter(meter_clip, soundMeter.clip);
+      }, 200);
     } else {
-      alert('The media stream contains an invalid amount of audio tracks.');
+      alert('The media stream contains an invalid amount of tracks:'
+         + audioTracks.length + ' audio ' + videoTracks.length + ' video');
       stream.stop();
     }
   }
@@ -65,6 +119,12 @@
   }
 
   function onload() {
+    try {
+      window.AudioContext = window.AudioContext || window.webkitAudioContext;
+      audioContext = new AudioContext();
+    } catch(e) {
+      alert('Web Audio API not found');
+    }
     audioElement = $('audio');
     buttonStart = $('start');
     buttonStop = $('stop');
@@ -72,37 +132,22 @@
     buttonStop.disabled = true;
   }
 
-  // Meter class that generates a number.
-  function SoundMeter() {
-    this.context = new webkitAudioContext();
-    this.volume = 0.0;
-  }
-
-  SoundMeter.prototype.connect = function(stream) {
-    console.log('SoundMeter connecting');
-    this.mic = this.context.createMediaStreamSource(stream);
-    this.script = this.context.createScriptProcessor(1024, 1, 1);
-    that = this;
-    this.script.onaudioprocess = function(event) {
-      var input = event.inputBuffer.getChannelData(0);
-      var i;
-      var sum = 0.0;
-      for (i = 0; i < input.length; ++i) {
-        sum += Math.abs(input[i]);
-      }
-      that.showVolume(sum / input.length);
-    }
-    console.log('Buffer size ' + this.script.bufferSize);
-    this.mic.connect(this.script);
-    // Necessary to make sample run, but should not be.
-    this.script.connect(this.context.destination)
-  }
-
-  SoundMeter.prototype.showVolume = function(volume) {
-    alert('Dummy showVolume called')
+  function paintMeter(context, number) {
+     context.clearRect(0, 0, 400, 20);
+     context.fillStyle = 'red';
+     context.fillRect(0, 0, number * 400, 20);
   }
 
 </script>
+<style>
+  button {
+    font: 14px sans-serif;
+    padding: 8px;
+  }
+  canvas {
+    border:1px solid #000000;
+  }
+</style>
 </head>
 
 <body onload="onload()">
@@ -111,16 +156,16 @@
      using WebAudio.<br>
      Press Start, select a microphone, listen to your own voice in loopback,
      and see the numbers change as you speak.</p>
-  <style>
-    button {
-      font: 14px sans-serif;
-      padding: 8px;
-    }
-  </style>
+     The "instant" volume changes approximately every 50 ms; the "slow"
+     volume approximates the average volume over about a second.
   <audio id="audio" autoplay="autoplay" controls="controls"></audio><br><br>
   <button id="start" onclick="start()">Start</button>
   <button id="stop" onclick="stop()">Stop</button><br><br>
   Volume (instant): <span id="volume">Not set</span><br>
-  Volume (slow): <span id="decaying_volume">Not set</span>
+  Volume (slow): <span id="decaying_volume">Not set</span><br>
+  <canvas id="graphic_volume" width="400" height="20"></canvas> Volume<br>
+  <canvas id="graphic_slow" width="400" height="20"></canvas> Slow<br>
+  <canvas id="graphic_clip" width="400" height="20"></canvas> Clipping
+
 </body>
 </html>