Script for parsing BPM

main.js

var audioobj = document.getElementsByTagName("audio")[0];
		// var text = document.getElementById("text");
		var actualBPM;
		var request = new XMLHttpRequest();
		console.log("Audio source: " + audioobj.src);
		request.open('GET', audioobj.src, true);
		request.responseType = 'arraybuffer';
		var targetspd = 1;

		request.onload = function() {
			console.log("Handling request now");
			//Create offline context
		  var OfflineContext = window.OfflineAudioContext || window.webkitOfflineAudioContext;
		  var offlineContext = new OfflineContext(1, 2, 44100);

		  offlineContext.decodeAudioData(request.response, function(buffer) {
				console.log("1");

		    // Create buffer source
				var source = offlineContext.createBufferSource();
		    source.buffer = buffer;

		    // Create filter
		    var filter = offlineContext.createBiquadFilter();
		    filter.type = "lowpass";

				console.log("2");
		    // Pipe the song into the filter, and the filter into the offline context
				source.connect(filter);
		    filter.connect(offlineContext.destination);

		    // Schedule the song to start playing at time:0
		    source.start(0);

		    var peaks,
		      initialThresold = 0.9,
		      thresold = initialThresold,
		      minThresold = 0.3,
		      minPeaks = 30;

				console.log("3");

				do {
				    peaks = getPeaksAtThreshold(buffer.getChannelData(0), thresold);
				    thresold -= 0.05;
				} while (peaks.length < minPeaks && thresold >= minThresold);

		    var intervals = countIntervalsBetweenNearbyPeaks(peaks);
		    var groups = groupNeighborsByTempo(intervals, buffer.sampleRate);

		    var top = groups.sort(function(intA, intB) {
		      return intB.count - intA.count;
		    }).splice(0, 5);

				// text.innerText=Math.round(top[0].tempo);
				actualBPM = Math.round(top[0].tempo);
				console.log("Actual BPM: " + actualBPM);
				audioobj.play();
				    var c = function() {
				      audioobj.playbackRate += (targetspd - audio.playbackRate) * 0.1;
				      //console.log("playbackrate " + audio.playbackRate);
				      var x = setTimeout(requestAnimationFrame(c), 1000 / 16);
				    }
				    c();

				  });
				};
				request.send();

				function countIntervalsBetweenNearbyPeaks(peaks) {
				  var intervalCounts = [];
				  peaks.forEach(function(peak, index) {
				    for (var i = 0; i < 10; i++) {
				      var interval = peaks[index + i] - peak;
				      var foundInterval = intervalCounts.some(function(intervalCount) {
				        if (intervalCount.interval === interval)
				          return intervalCount.count++;
				      });


				     if (!foundInterval) {
				        intervalCounts.push({
				          interval: interval,
				          count: 1
				        });
				      }
				    }
				  });
				  return intervalCounts;
				}

				function groupNeighborsByTempo(intervalCounts, sampleRate) {
				  var tempoCounts = [];

					intervalCounts.forEach(function(intervalCount, i) {
			    if (intervalCount.interval !== 0) {
		      	// Convert an interval to tempo
		      	var theoreticalTempo = 60 / (intervalCount.interval / sampleRate);

		      	// Adjust the tempo to fit within the 90-180 BPM range
				   	while (theoreticalTempo < 90) theoreticalTempo *= 2;
				    while (theoreticalTempo > 180) theoreticalTempo /= 2;

			      theoreticalTempo = Math.round(theoreticalTempo);
			      var foundTempo = tempoCounts.some(function(tempoCount) {
			        if (tempoCount.tempo === theoreticalTempo)
			          return tempoCount.count += intervalCount.count;
			      });
			      if (!foundTempo) {
			        tempoCounts.push({
			          tempo: theoreticalTempo,
			          count: intervalCount.count
			        });
			      }
			    }
			  });

				return tempoCounts;
			}

			function getPeaksAtThreshold(data, threshold) {
			  var peaksArray = [];
			  var length = data.length;
			  for (var i = 0; i < length;) {
			    if (data[i] > threshold) {
			      peaksArray.push(i);
			      // Skip forward ~ 1/4s to get past this peak.
			      i += 10000;
			    }
					i++;
			  }
			  return peaksArray;
			}

			var socket = io('http://localhost:3001');
			socket.on('kinect', function(msg) {
			  var bpm = Number(msg);
			//  $("#disp").text(bpm);
				console.log("New bpm: " + bpm);
				targetspd = bpm / actualBPM; //Number($("#text").text());
			})