Tighten up webrtc audio tests.

content/test/data/media/webrtc_test_audio.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 // Audio test utilities.
 
 // Gathers |numSamples| samples at |frequency| number of times per second and
 // calls back |callback| with an array with numbers in the [0, 32768] range.
 function gatherAudioLevelSamples(peerConnection, numSamples, frequency,
                                  callback) {
   console.log('Gathering ' + numSamples + ' audio samples...');
   var audioLevelSamples = []
   var gatherSamples = setInterval(function() {
     peerConnection.getStats(function(response) {
       audioLevelSamples.push(getAudioLevelFromStats_(response));
       if (audioLevelSamples.length == numSamples) {
         console.log('Gathered all samples.');
         clearInterval(gatherSamples);
         callback(audioLevelSamples);
       }
     });
   }, 1000 / frequency);
 }
 
 // Tries to identify the beep-every-second signal generated by the fake audio
 // media/audio/fake_audio_input_stream.cc. Fails the test if we can't see a
-// signal.
+// signal. The samples should have been gathered over at least three seconds
+// since we expect to see at least two "peaks" in there.
 function verifyAudioIsPlaying(samples) {
-  var average = 0;
-  for (var i = 0; i < samples.length; ++i)
-    average += samples[i] / samples.length;
+  var numPeaks = 0;
+  var maxLevel = 32768;

[perkj_chrome, 2014/03/28 13:29:17]

where to this numbers come frome? What do they mean?  Can you document? 

[phoglund_chromium, 2014/03/28 13:55:26]

Done.

+  var threshold = maxLevel * 0.8;
+  var currentlyOverThreshold = false;
+
+  // Detect when we have been been over the threshold and is going back again
+  // (i.e. count peaks). We should see about one peak per second.
+  for (var i = 0; i < samples.length; ++i) {
+    if (currentlyOverThreshold && samples[i] < threshold)
+      numPeaks++;
+    currentlyOverThreshold = samples[i] >= threshold;
+  }
 
   var largest = 0;
   for (var i = 0; i < samples.length; ++i)
     largest = Math.max(largest, samples[i]);
 
-  console.log('Average audio level: ' + average + ', largest: ' + largest);
+  console.log('Number of peaks identified: ' + numPeaks + ', max: ' + largest);
 
-  // TODO(phoglund): Make a more sophisticated curve-fitting algorithm. We want
-  // to see a number of peaks with relative silence between them. The following
-  // seems to work fine on a nexus 7.
-  if (average < 3000 || average > 8000)
-    failTest('Unexpected avg audio level: got ' + average + ', expected it ' +
-             'to be 4000 < avg < 8000.');
+  if (numPeaks < 2)
+    failTest('Expected to see at least two peaks in audio signal, got ' +
+        numPeaks + '. Dumping samples for analysis: "' + samples + '"');
+
   if (largest < 25000)
-    failTest('Too low max audio level: got ' + largest + ', expected > 30000.');
+    failTest('Too low max audio level: got ' + largest + ', expected > 25000.');
 }
 
 // If silent (like when muted), we should get very near zero audio level.
 function verifyIsSilent(samples) {
   var average = 0;
   for (var i = 0; i < samples.length; ++i)
     average += samples[i] / samples.length;
 
   console.log('Average audio level: ' + average);
   if (average > 500)
@@ skipping 10 matching lines @@
     var report = reports[i];
     if (report.names().indexOf('audioOutputLevel') != -1) {
       audioOutputLevels.push(report.stat('audioOutputLevel'));
     }
   }
   // Should only be one audio level reported, otherwise we get confused.
   assertEquals(1, audioOutputLevels.length);
 
   return audioOutputLevels[0];
 }