Create a waveform of the full track with Web Audio API

Question

Realtime moving Waveform

I\'m currently playing with Web Audio API and made a spectrum using canvas.

Answer 1

// AUDIO CONTEXT
window.AudioContext = (window.AudioContext || 
window.webkitAudioContext || 
window.mozAudioContext || 
window.oAudioContext || 
window.msAudioContext);

if (!AudioContext) alert('This site cannot be run in your Browser. Try a recent Chrome or Firefox. ');

var audioContext = new AudioContext();
var currentBuffer  = null;

// CANVAS
var canvasWidth = window.innerWidth,  canvasHeight = 120 ;
var newCanvas   = createCanvas (canvasWidth, canvasHeight);
var context     = null;

window.onload = appendCanvas;
function appendCanvas() { document.body.appendChild(newCanvas);
                          context = newCanvas.getContext('2d'); }

// MUSIC LOADER + DECODE
function loadMusic(url) {   
    var req = new XMLHttpRequest();
    req.open( "GET", url, true );
    req.responseType = "arraybuffer";    
    req.onreadystatechange = function (e) {
          if (req.readyState == 4) {
             if(req.status == 200)
                  audioContext.decodeAudioData(req.response, 
                    function(buffer) {
                             currentBuffer = buffer;
                             displayBuffer(buffer);
                    }, onDecodeError);
             else
                  alert('error during the load.Wrong url or cross origin issue');
          }
    } ;
    req.send();
}

function onDecodeError() {  alert('error while decoding your file.');  }

// MUSIC DISPLAY
function displayBuffer(buff /* is an AudioBuffer */) {
  
  var drawLines = 500;
   var leftChannel = buff.getChannelData(0); // Float32Array describing left channel     
   var lineOpacity = canvasWidth / leftChannel.length  ;      
   context.save();
   context.fillStyle = '#080808' ;
   context.fillRect(0,0,canvasWidth,canvasHeight );
   context.strokeStyle = '#46a0ba';
   context.globalCompositeOperation = 'lighter';
   context.translate(0,canvasHeight / 2);
   //context.globalAlpha = 0.6 ; // lineOpacity ;
   context.lineWidth=1;
   var totallength = leftChannel.length;
   var eachBlock = Math.floor(totallength / drawLines);
   var lineGap = (canvasWidth/drawLines);

  context.beginPath();
   for(var i=0;i<=drawLines;i++){
      var audioBuffKey = Math.floor(eachBlock * i);
       var x = i*lineGap;
       var y = leftChannel[audioBuffKey] * canvasHeight / 2;
       context.moveTo( x, y );
       context.lineTo( x, (y*-1) );
   }
   context.stroke();
   context.restore();
}

function createCanvas ( w, h ) {
    var newCanvas = document.createElement('canvas');
    newCanvas.width  = w;     newCanvas.height = h;
    return newCanvas;
};


loadMusic('https://raw.githubusercontent.com/katspaugh/wavesurfer.js/master/example/media/demo.wav');