Audio Fingerprinting指纹获取核心代码

  浏览器的音频指纹识别-现在是FingerprintJS2的一部分，附上获取Audio Fingerprinting指纹获取核心代码

  

var audioFingerprint = (function () {
	
	var context = null;
	var currentTime = null;
	var oscillator = null;
	var compressor = null;
	var fingerprint = null;
	var callback = null
	
	function run(cb, debug = false) {
		
		callback = cb;
		
		try {
			
			setup();
		
			oscillator.connect(compressor);
			compressor.connect(context.destination);
		
			oscillator.start(0);
			context.startRendering();
			
			context.oncomplete = onComplete;
		  
		} catch (e) {
			
			if (debug) {
				throw e;
			}
			
		}
	}
	
	function setup()
	{
		setContext();
		currentTime = context.currentTime;
		setOscillator();
		setCompressor();
	}

	function setContext()
	{
		var audioContext = window.OfflineAudioContext || window.webkitOfflineAudioContext;
		context = new audioContext(1, 44100, 44100);
	}

	function setOscillator()
	{
		oscillator = context.createOscillator();
		oscillator.type = "triangle";
		oscillator.frequency.setValueAtTime(10000, currentTime);
	}

	function setCompressor()
	{
		compressor = context.createDynamicsCompressor();
		
		setCompressorValueIfDefined('threshold', -50);
		setCompressorValueIfDefined('knee', 40);
		setCompressorValueIfDefined('ratio', 12);
		setCompressorValueIfDefined('reduction', -20);
		setCompressorValueIfDefined('attack', 0);
		setCompressorValueIfDefined('release', .25);
	}

	function setCompressorValueIfDefined(item, value)
	{
		if (compressor[item] !== undefined && typeof compressor[item].setValueAtTime === 'function') {
			compressor[item].setValueAtTime(value, context.currentTime);
		}
	}
	
	function onComplete(event)
	{
		generateFingerprints(event);
	    compressor.disconnect();
	}
	
	function generateFingerprints(event)
	{
		var output = null;
		for (var i = 4500; 5e3 > i; i++) {
			
			var channelData = event.renderedBuffer.getChannelData(0)[i];
			output += Math.abs(channelData);
			
		}
		
		fingerprint = output.toString();
		
		if (typeof callback === 'function') {
			return callback(fingerprint);
		}
	}
	
	return {
		run:run
	};
	
})();