pleroma-fe-sjw/instance/pleroma-mods/pleroma-mod-tracker/audio-player.js

function AudioPlayer( callback, effect ) {
  var AudioContext = window.AudioContext || window.webkitAudioContext;
  var audioContext = new AudioContext();
  var scriptProcessor = audioContext.createScriptProcessor( 0, 0, 2 );
  var audioSource = new SineSource( audioContext.sampleRate );
  var gainNode = audioContext.createGain();
  gainNode.gain.value = localStorage.getItem('volume') === null ? 0.25 : localStorage.getItem('volume');
  gainNode.connect( audioContext.destination );
  
  var onaudioprocess = function( event ) {
    var count = event.outputBuffer.length;
    if( callback ) {
      callback( count );
    }
    var leftBuf = event.outputBuffer.getChannelData( 0 );
    var rightBuf = event.outputBuffer.getChannelData( 1 );
    audioSource.getAudio( leftBuf, rightBuf, count );
    if( effect ) {
      effect( leftBuf, rightBuf, count );
    }
  }
  this.getSamplingRate = function() {
    return audioContext.sampleRate;
  }
  this.setAudioSource = function( audioSrc ) {
    audioSource = audioSrc;
  }
  this.play = function() {
    audioContext.resume().then(() => {
      scriptProcessor.onaudioprocess = onaudioprocess;
      scriptProcessor.connect( gainNode );
    });
  }
  this.stop = function() {
    if( scriptProcessor.onaudioprocess ) {
      scriptProcessor.disconnect( gainNode );
      scriptProcessor.onaudioprocess = null;
    }
  }
  this.setVolume = function( volume ) {
    gainNode.gain.value = volume;
  }
}

function SineSource( samplingRate ) {
  // Simple AudioSource for testing.
  var rate = samplingRate;
  var freq = 2 * Math.PI * 440 / rate;
  var phase = 0;
  this.getSamplingRate = function() {
    return rate;
  }
  this.getAudio = function( leftBuffer, rightBuffer, count ) {
    for( var idx = 0; idx < count; idx++, phase++ ) {
      leftBuffer[ idx ] = Math.sin( phase * freq );
      rightBuffer[ idx ] = Math.sin( phase * freq * 0.5 );
    }
  }
}