Deflake preservesPitch tests

This CL changes preservesPitch tests to wait until the audioElement's
currentTime is at least 0.5 seconds before trying to detect the pitch.
Without this check, the test can try to detect the pitch before the
audio has played enough, which can return a dominant frequency of 0Hz
and fail the test.

The CL also makes a few stylistic changes, and fixes an off-by-one error
in the number of increments used to calculate frequencies.

Bug: 1096238
Change-Id: I6e98e172862a47bea1c4026737138293914f7906
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2298281
Auto-Submit: Thomas Guilbert <tguilbert@chromium.org>
Commit-Queue: Philip Jägenstedt <foolip@chromium.org>
Reviewed-by: Philip Jägenstedt <foolip@chromium.org>
Cr-Commit-Position: refs/heads/master@{#788535}

third_party/blink/web_tests/external/wpt/html/semantics/embedded-content/media-elements/pitch-detector.js

@@ -16,14 +16,15 @@ function getPitchDetector(media, t) {
   sourceNode.connect(analyser);
   analyser.connect(audioContext.destination);
 
-  // Returns the frequency value for the nth FFT bin.
-  var binConverter = (bin) => audioContext.sampleRate*(bin/FFT_SIZE);
-
-  return () => getPitch(analyser, binConverter);
+  return () => getPitch(analyser);
 }
 
-function getPitch(analyser, binConverter) {
-  var buf = new Uint8Array(FFT_SIZE/2);
+function getPitch(analyser) {
+  // Returns the frequency value for the nth FFT bin.
+  var binConverter = (bin) =>
+    (analyser.context.sampleRate/2)*((bin)/(analyser.frequencyBinCount-1));
+
+  var buf = new Uint8Array(analyser.frequencyBinCount);
   analyser.getByteFrequencyData(buf);
   return findDominantFrequency(buf, binConverter);
 }
@@ -40,9 +41,8 @@ function findDominantFrequency(buf, binConverter) {
     }
   }
 
-  // The distance between bins is always constant and corresponds to
-  // (1/FFT_SIZE)th of the sample rate. Use the frequency value of the 1st bin
-  // as the margin directly, instead of calculating an average from the values
-  // of the neighboring bins.
+  // The spread of frequencies within bins is constant and corresponds to
+  // (1/(FFT_SIZE-1))th of the sample rate. Use the value of bin #1 as a
+  // shorthand for that value.
   return { value:binConverter(bin), margin:binConverter(1) };
 }
\ No newline at end of file

third_party/blink/web_tests/external/wpt/html/semantics/embedded-content/media-elements/preserves-pitch.html

@@ -56,27 +56,34 @@ function testPreservesPitch(preservesPitch, playbackRate, expectedPitch, descrip
         audio.playbackRate = playbackRate;
         setPreservesPitch(audio, preservesPitch);
 
-        function promiseTimeUpdate() {
-            return new Promise((resolve) => audio.ontimeupdate = resolve);
+        function waitUntil(time) {
+            return new Promise((resolve) => {
+                audio.ontimeupdate = () => {
+                    if (audio.currentTime >= time) {
+                        resolve();
+                    }
+                };
+            });
         }
 
-        function verifyPitch() {
-            var pitch = detector();
+        await test_driver.bless("Play audio element", () => audio.play() )
 
-            // 25Hz is larger than the margin we get from 48kHz and 44.1kHz
-            // audio being analyzed by a FFT of size 2048. If we get something
-            // different, there is an error within the test's calculations (or
-            // we might be dealing a larger sample rate).
-            assert_less_than(pitch.margin, 25,
-                "Test error: the margin should be reasonably small.")
+        // Wait until we have at least played some audio. Otherwise, the
+        // detector might return a pitch of 0Hz.
+        await waitUntil(0.5);
 
-            assert_approx_equals(pitch.value, expectedPitch, pitch.margin,
-                "The actual pitch should be close to the expected pitch.");
-        }
+        var pitch = detector();
+
+        // 25Hz is larger than the margin we get from 48kHz and 44.1kHz
+        // audio being analyzed by a FFT of size 2048. If we get something
+        // different, there is an error within the test's calculations (or
+        // we might be dealing a larger sample rate).
+        assert_less_than(pitch.margin, 25,
+            "Test error: the margin should be reasonably small.")
+
+        assert_approx_equals(pitch.value, expectedPitch, pitch.margin,
+            "The actual pitch should be close to the expected pitch.");
 
-        await test_driver.bless("Play audio element", () => audio.play() )
-          .then(promiseTimeUpdate)
-          .then(verifyPitch);
     }, description);
 }