Bug 1694085 - Smooth the FFT analysis to make the test more robust.

Differential Revision: https://phabricator.services.mozilla.com/D129145

Author: padenot

dom/media/mediasource/test/test_HEAAC_extradata.html

@@ -33,7 +33,6 @@
   await ac.resume();
   const mediaElementSource = ac.createMediaElementSource(element);
   const analyser = new AnalyserNode(ac);
-  analyser.smoothingTimeConstant = 0.0;
 
   // Undo the volume scaling applied globally during test. This is fine because
   // the audio isn't routed to an actual audio output device in this test, it's
@@ -55,7 +54,7 @@
   analyser.getFloatFrequencyData(spectrum);
   const indexFor15kHz =
     binIndexForFrequency(15000, analyser.fftSize, ac.sampleRate);
-  ok(spectrum[indexFor15kHz] > -50,
+  ok(spectrum[indexFor15kHz] > -60,
       `Energy present at 15kHz (bin index: ${indexFor15kHz}) when playing white
        noise encoded in HE-AAC ${spectrum[indexFor15kHz]}`);
 }