Created
March 11, 2012 08:36
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Web Audio API overview post
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| <body> | |
| <div id="container"> | |
| <canvas height="200" width="500" id="fft"></canvas> | |
| <audio id="audio" src="IO2010.mp3" preload controls></audio> | |
| </div> | |
| <script> | |
| // requestAnim shim layer by Paul Irish | |
| window.requestAnimFrame = (function(){ | |
| return window.requestAnimationFrame || | |
| window.webkitRequestAnimationFrame || | |
| window.mozRequestAnimationFrame || | |
| window.oRequestAnimationFrame || | |
| window.msRequestAnimationFrame || | |
| function(callback, element){ | |
| window.setTimeout(callback, 1000 / 60); | |
| }; | |
| })(); | |
| </script> | |
| <script> | |
| // Some Javascript | |
| </script> | |
| </body> |
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| <p>LowPass: <input id="lowpass" type="range" value="5000" min="0" max="5000" step="10"></p> | |
| <script> | |
| function init() { | |
| source = audioContext.createMediaElementSource(audioElement); | |
| gain = audioContext.createGainNode(); | |
| filter = audioContext.createLowPass2Filter(); | |
| filter.cutoff.value = 22050; | |
| analyser = audioContext.createAnalyser(); | |
| source.connect(gain); | |
| gain.connect(filter); | |
| filter.connect(analyser); | |
| analyser.connect(audioContext.destination); | |
| draw(); | |
| } | |
| document.getElementById("lowpass").addEventListener('change', | |
| function(e){ | |
| filter.cutoff.value = this.value | |
| }); | |
| </script> |
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| <p>Gain: <input id="gain" type="range" value="1" min="0" max="1" step="0.01"></p> |
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| source = audioContext.createMediaElementSource(audioElement); | |
| gain = audioContext.createGainNode(); | |
| analyser = audioContext.createAnalyser(); | |
| source.connect(gain); | |
| gain.connect(analyser); | |
| analyser.connect(audioContext.destination); |
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| document.getElementById("gain").addEventListener('change', | |
| function(e){ | |
| gain.gain.value = this.value | |
| }); |
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| gradient = ctx.createLinearGradient(0, 0, 0, canvas.height); | |
| gradient.addColorStop(0, "rgba(255, 0, 0, 1)"); | |
| gradient.addColorStop(0.15, "rgba(255, 255, 0, 1)"); | |
| gradient.addColorStop(0.3, "rgba(0, 255, 0, 1)"); | |
| gradient.addColorStop(0.5, "rgba(0, 255, 255, 1)"); | |
| gradient.addColorStop(0.65, "rgba(0, 0, 255, 1)"); | |
| gradient.addColorStop(0.8, "rgba(255, 0, 255, 1)"); | |
| gradient.addColorStop(1, "rgba(255, 0, 0, 1)"); | |
| ctx.fillStyle = gradient; |
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| // The audio element | |
| audioElement = document.getElementById('audio'); | |
| // The canvas, its context and fillstyle | |
| canvas = document.getElementById('fft'); | |
| ctx = canvas.getContext('2d'); | |
| ctx.fillStyle = "white"; | |
| // Create new Audio Context and an audio analyzer | |
| audioContext = new webkitAudioContext(); | |
| analyser = audioContext.createAnalyser(); | |
| // Canvas' height and width | |
| CANVAS_HEIGHT = canvas.height; | |
| CANVAS_WIDTH = canvas.width; | |
| // We'll need the offset later | |
| OFFSET = 100; | |
| // Spacing between the individual bars | |
| SPACING = 10; | |
| // Initialize and start drawing | |
| // when the audio starts playing | |
| window.onload = init; | |
| audioElement.addEventListener('play', draw); | |
| function init() { | |
| // Take input from audioElement | |
| source = audioContext.createMediaElementSource(audioElement); | |
| // Connect the stream to an analyzer | |
| source.connect(analyser); | |
| // Connect the analyzer to the speakers | |
| analyser.connect(audioContext.destination); | |
| // Start the animation | |
| draw(); | |
| } | |
| function draw() { | |
| // See http://paulirish.com/2011/requestanimationframe-for-smart-animating/ | |
| requestAnimFrame(draw, canvas); | |
| // New typed array for the raw frequency data | |
| freqData = new Uint8Array(analyser.frequencyBinCount); | |
| // Put the raw frequency into the newly created array | |
| analyser.getByteFrequencyData(freqData); | |
| // Clear the canvas | |
| ctx.clearRect(0, 0, CANVAS_WIDTH, CANVAS_HEIGHT); | |
| // This loop draws all the bars | |
| for (var i = 0; i < freqData.length - OFFSET; i++) { | |
| // Work out the hight of the current bar | |
| // by getting the current frequency | |
| var magnitude = freqData[i + OFFSET]; | |
| // Draw a bar from the bottom up (cause for the "-magnitude") | |
| ctx.fillRect(i * SPACING, CANVAS_HEIGHT, SPACING / 2, -magnitude); | |
| }; | |
| } |
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