Javascript Web Audio API AnalyserNode Not Working
Question
The code is supposed to stream any url and provide a visualization of the audio. Unfortunately, the visualizer is not working. The visualization relies on the data from the AnalyzerNode, which is always returning empty data. Why doesn't the AnalyserNode in this code work? The numberOfOutputs on the source node increases after I .connect() them, but the numberOfInputs on the AnalyserNode does not change.
<html>
<head>
<script>
var context;
var source;
var analyser;
var canvas;
var canvasContext;
window.addEventListener('load', init, false);
function init() {
try {
// Fix up for prefixing
window.AudioContext = window.AudioContext || window.webkitAudioContext;
window.requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame ||
window.webkitRequestAnimationFrame || window.msRequestAnimationFrame;
context = new AudioContext();
analyser = context.createAnalyser();
canvas = document.getElementById("analyser");
canvasContext = canvas.getContext('2d');
}
catch(e) {
alert(e);
alert('Web Audio API is not supported in this browser');
}
}
function streamSound(url) {
var audio = new Audio();
audio.src = url;
audio.controls = true;
audio.autoplay = true;
source = context.createMediaElementSource(audio);
source.connect(analyser);
analyser.connect(context.destination);
document.body.appendChild(document.createElement('br'));
document.body.appendChild(audio);
render();
}
function render(){
window.requestAnimationFrame(render);
//Get the Sound data
var freqByteData = new Uint8Array(analyser.frequencyBinCount);
analyser.getByteFrequencyData(freqByteData);
//we Clear the Canvas
canvasContext.clearRect(0, 0, canvas.width, canvas.height);
//draw visualization
for(var i=0;i<analyser.frequencyBinCount;i++){
canvasContext.fillRect(i*2,canvas.height,1,-freqByteData[i]);
//Data seems to always be zero
if(freqByteData[i] != 0) {
alert(freqByteData[i]);
}
}
}
</script>
</head>
<body>
<button onclick="streamSound(document.getElementById('url').value)"> Stream sound</button>
<input id="url" size='77' value="Enter a URL to Stream">
<br />
<canvas id="analyser" width="600" height="200"></canvas>
</body>
</html>
1 answers
solution1
3 ACCPTED 2013-05-17 04:05:14
You should setup an event listener for the audio's canplay event and only setup the MediaElementSource and connect it after that event fires.
It also won't work in Safari due to a bug in their implementation . AFAIK Chrome is the only browser that properly supports the Web Audio API.
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