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BeatDetector.js
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BeatDetector.js
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'use strict';
angular
.module('hackday')
.factory('BeatDetector', function($q) {
return {
convertIndexToTime: convertIndexToTime,
drawBeats: drawBeats,
exportPeakBuffers: exportPeakBuffers,
getPeaks: getPeaks,
lowPassFilter: lowPassFilter
};
function lowPassFilter(buffer) {
const ctx = new OfflineAudioContext(1, buffer.length, buffer.sampleRate),
source = ctx.createBufferSource(),
filter = ctx.createBiquadFilter();
source.buffer = buffer;
filter.type = "lowpass";
source.connect(filter);
filter.connect(ctx.destination);
source.start(0);
return ctx.startRendering();
}
function getPeaks(buffer, threshold) {
const channel = buffer.getChannelData(0),
peaks = [];
for (let i = 0; i < channel.length;) {
if (channel[i] > threshold) {
peaks.push(i);
i += 10000;
} else {
i++;
}
}
return peaks;
}
function drawBeats(peaks, length) {
const ctx = document.querySelectorAll('#waveform').item(0).getContext('2d'),
width = ctx.canvas.width;
ctx.clearRect(0, 0, ctx.canvas.width, ctx.canvas.height);
ctx.strokeStyle = '#5397CC';
for (let i = 0; i < peaks.length; i++) {
ctx.beginPath();
ctx.moveTo(peaks[i] / length * width, 0);
ctx.lineTo(peaks[i] / length * width, ctx.canvas.height);
ctx.stroke();
}
}
function convertIndexToTime(peaks, audioBuffer) {
return peaks.map(function(peak) {
return peak / audioBuffer.getChannelData(0).length * audioBuffer.duration;
})
}
function exportPeakBuffers(peaks, buffer) {
const timestamp = convertIndexToTime(peaks, buffer);
return $q.all(_.map(peaks, function(peak) {
return exportPeakBuffer(peak, buffer);
}));
}
function exportPeakBuffer(peak, buffer) {
const ctx = new OfflineAudioContext(1, 1 * buffer.sampleRate, buffer.sampleRate),
source = ctx.createBufferSource();
source.buffer = buffer,
source.start(0, Math.max(peak - 0.3, 0), 1);
source.connect(ctx.destination);
return ctx.startRendering().then(function(buffer){
return {peak: peak, buffer: buffer};
});
}
});