Print out audio levels for all video / audio elements on the page

audio-levels.js

// audio-levels.js
// https://github.com/bgrins/devtools-snippets
// Print out audio levels for all video / audio elements on the page.

// Watch out for: "MediaElementAudioSource outputs zeroes due to CORS access restrictions" ...for x-origin media urls

(function() {

	[].forEach.call(document.querySelectorAll("video,audio"), function(media) {
        var splitPath = media.src.split('/');
		var srcName = media.id +'_'+ splitPath[splitPath.length-1];
		
		var context = window.__webkitAudioContext = window.__webkitAudioContext || new webkitAudioContext();
		var jsProcessor;
		var source;

		var frameBufferSize = 4096;
		var bufferSize = frameBufferSize/4;
		var signal = new Float32Array(bufferSize);
		
		var processTotal = 5;
		var processCount = processTotal;
        
		//connect html5 media element to web audio context
		try {
			source = media.__elementSource = media.__elementSource || context.createMediaElementSource(media);
		}
		catch(e) {
			console.error("Cannot create Media Element Source for element", media, e);
			return;
		}
		
		console.group('Audio Levels for '+ srcName);
		
		var sum = 0;
		
		//amplitude js processor
		try {
			jsProcessor = context.createScriptProcessor(2048);
		}
		catch(e) {
			console.error("Cannot create Script Processor for Audio Context", context, e);
			return;
		}
		
		jsProcessor.onaudioprocess = function audioAvailable(event) {
		
			// Copy input arrays to output arrays to play sound
			var inputArrayL = event.inputBuffer.getChannelData(0);
			var inputArrayR = event.inputBuffer.getChannelData(1);
			var outputArrayL = event.outputBuffer.getChannelData(0);
			var outputArrayR = event.outputBuffer.getChannelData(1);
			
			var value = 0;
			var max = 0;
			var n = inputArrayL.length;
			for (var i = 0; i < n; ++i) {
				outputArrayL[i] = inputArrayL[i];
				outputArrayR[i] = inputArrayR[i];
				// create data frame for fft - deinterleave and mix down to mono
				value = (inputArrayL[i] + inputArrayR[i]) / 2;
				signal[i] = value;
				max = Math.max(Math.abs(value));
			}

			console.log('samples:', n, 'max signal strength:', max, 'at position:', context.currentTime);
			
			sum += max;
			
			// tear down
			if (--processCount === 0) {
				jsProcessor.onaudioprocess = null;
				jsProcessor.disconnect(0);
				//source.disconnect(0);
				//source.connect(context.destination);
				
				console.log('Level 0-100:', (sum * 100 / processTotal).toFixed(2));
				
				console.groupEnd('Audio Levels for '+ srcName);
			}
		};
		
		//connect graph
		source.connect(jsProcessor);
		source.connect(context.destination);
		jsProcessor.connect(context.destination);
		
		
	});
})();