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// This should be removed when the webaudio/historical.html tests are passing.
// Tracking bug: https://bugs.webkit.org/show_bug.cgi?id=204719
window.AudioContext = window.AudioContext || window.webkitAudioContext;
var FFT_SIZE = 2048;
var audioContext;
var sourceNode;
function getPitchDetector(media) {
if(!audioContext) {
audioContext = new AudioContext();
sourceNode = audioContext.createMediaElementSource(media);
}
var analyser = audioContext.createAnalyser();
analyser.fftSize = FFT_SIZE;
sourceNode.connect(analyser);
analyser.connect(audioContext.destination);
return {
ensureStart() { return audioContext.resume(); },
detect() { return getPitch(analyser); },
cleanup() {
sourceNode.disconnect();
analyser.disconnect();
},
};
}
function getPitch(analyser) {
// Returns the frequency value for the nth FFT bin.
var binConverter = (bin) =>
(audioContext.sampleRate/2)*((bin)/(analyser.frequencyBinCount-1));
var buf = new Uint8Array(analyser.frequencyBinCount);
analyser.getByteFrequencyData(buf);
return findDominantFrequency(buf, binConverter);
}
// Returns the dominant frequency, +/- a certain margin.
function findDominantFrequency(buf, binConverter) {
var max = 0;
var bin = 0;
for (var i=0;i<buf.length;i++) {
if(buf[i] > max) {
max = buf[i];
bin = i;
}
}
// 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) };
}
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