Possible to analyze streaming audio from Icecast using Web Audio API and createMediaElementSource?

Question

Using the Web Audio API and createMediaElement method you can use a typed array to get frequency data from audio playback in an <audio> element and it works in most browsers as long as the source URL is local (not streaming). See Codepen: http://codepen.io/soulwire/pen/Dscga

Actual Code:

var audioCtx = new (window.AudioContext || window.webkitAudioContext)();
var audioElement = new Audio('http://crossorigin.me/http://87.230.103.9:80/top100station.mp3'); // example stream

audioElement.crossOrigin = 'anonymous';
audioElement.type = 'audio/mpeg';

var analyser = audioCtx.createAnalyser();

audioElement.addEventListener('canplay', function() {
  var audioSrc = audioCtx.createMediaElementSource(audioElement);
  // Bind our analyser to the media element source.
  audioSrc.connect(analyser);
  audioSrc.connect(audioCtx.destination);
});

var frequencyData = new Uint8Array(20);

var svgHeight = ($window.innerHeight / 2) - 20;
var svgWidth = $window.innerWidth - 20;
var barPadding = '2';

function createSvg(parent, height, width) {
  return d3.select(parent).append('svg').attr('height', height).attr('width', width);
}

var svg = createSvg('.visualizer', svgHeight, svgWidth);

// Create our initial D3 chart.
svg.selectAll('rect')
   .data(frequencyData)
   .enter()
   .append('rect')
   .attr('x', function (d, i) {
      return i * (svgWidth / frequencyData.length);
   })
   .attr('width', svgWidth / frequencyData.length - barPadding);

// Continuously loop and update chart with frequency data.
function renderChart() {
   requestAnimationFrame(renderChart);

   // Copy frequency data to frequencyData array.
   analyser.getByteFrequencyData(frequencyData);

   console.log(frequencyData);

   // Update d3 chart with new data.
   svg.selectAll('rect')
      .data(frequencyData)
      .attr('y', function(d) {
         return svgHeight - d;
      })
      .attr('height', function(d) {
        return d;
      })
      .style('opacity', function(d) {
        return d / 255;
      })
      .attr('fill', function() {
         return 'rgb(255, 255, 255)';
      });
}

// Run the loop
renderChart();

Where .visualizer is an empty <div>

I'm developing a hybrid app for a radio station using Ionic/Angular and the audio stream is through Icecast (http://dir.xiph.org/) and I've run into the following issue: local mp3s are analyzed and visualized no problem however if you use the streaming URL, analyser.getByteFrequencyData is all zeroes in iOS Safari but it plays fine.

So to recap:

I know there was a bug in earlier versions of Safari where createMediaElementSource() would fail but if that were still the case then it wouldn't work on the local file?

Any ideas?

Answer 1

Still not working with Safari and iOS Chrome (which is using Apple WebKit?). Other browsers seem to be fine now. Audio plays fine, CORS is ok - yet Analyser is not working.

This fiddle (not mine) demonstrates the behavior well. Latter uri gets analysed, former not:

  const url = useStream
  ? 'https://c2.radioboss.fm:18071/stream'
  : 'https://twgljs.org/examples/sounds/DOCTOR%20VOX%20-%20Level%20Up.mp3';

Related question in Apple forum (no answers)

Answer 2

It just is not implemented according to the specs in Safari and will return an array of zeroes instead of frequencies for streams. Many people have observed this behaviour, e.g. http://isflashdeadyet.com/tests/web-audio-visualization/index-analyser.html and https://github.com/Okazari/Rythm.js/issues/7

It is supposted to work according to https://browsersupport.io/AnalyserNode.prototype.getByteFrequencyData

Here you will find that "Safari [is] seemingly reporting no signal (a value of 128) across the board when requesting byte data on an AnalyserNode": http://fourthof5.com/audio-visualisation-with-the-web-audio-api

Test the demo here to see the current status: http://fourthof5.com/assets/posts/audio-visualisation-with-the-web-audio-api/index.html