fujiconvert/waveWorker.js at master · lybrown/fujiconvert · GitHub

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// https://stackoverflow.com/questions/22560413/html5-web-audio-convert-audio-buffer-into-wav-file
// Author: https://stackoverflow.com/users/993683/joe
self.onmessage = function( e ){
  var wavPCM = new WavePCM( e['data']['config'] );
  wavPCM.record( e['data']['pcmArrays'] );
  wavPCM.requestData();
};

var WavePCM = function( config ){
  this.sampleRate = config['sampleRate'] || 48000;
  this.bitDepth = config['bitDepth'] || 16;
  this.recordedBuffers = [];
  this.bytesPerSample = this.bitDepth / 8;
};

WavePCM.prototype.record = function( buffers ){
  this.numberOfChannels = this.numberOfChannels || buffers.length;
  var bufferLength = buffers[0].length;
  var reducedData = new Uint8Array( bufferLength * this.numberOfChannels * this.bytesPerSample );

  // Interleave
  for ( var i = 0; i < bufferLength; i++ ) {
    for ( var channel = 0; channel < this.numberOfChannels; channel++ ) {

      var outputIndex = ( i * this.numberOfChannels + channel ) * this.bytesPerSample;
      var sample = buffers[ channel ][ i ];

      // Check for clipping
      if ( sample > 1 ) {
        sample = 0.999999999;
      }

      else if ( sample < -1 ) {
        sample = -1;
      }

      // bit reduce and convert to uInt
      switch ( this.bytesPerSample ) {
        case 4:
          sample = sample * 2147483648;
          reducedData[ outputIndex ] = sample;
          reducedData[ outputIndex + 1 ] = sample >> 8;
          reducedData[ outputIndex + 2 ] = sample >> 16;
          reducedData[ outputIndex + 3 ] = sample >> 24;
          break;

        case 3:
          sample = sample * 8388608;
          reducedData[ outputIndex ] = sample;
          reducedData[ outputIndex + 1 ] = sample >> 8;
          reducedData[ outputIndex + 2 ] = sample >> 16;
          break;

        case 2:
          sample = sample * 32768;
          reducedData[ outputIndex ] = sample;
          reducedData[ outputIndex + 1 ] = sample >> 8;
          break;

        case 1:
          reducedData[ outputIndex ] = ( sample + 1 ) * 128;
          break;

        default:
          throw "Only 8, 16, 24 and 32 bits per sample are supported";
      }
    }
  }

  this.recordedBuffers.push( reducedData );
};

WavePCM.prototype.requestData = function(){
  var bufferLength = this.recordedBuffers[0].length;
  var dataLength = this.recordedBuffers.length * bufferLength;
  var headerLength = 44;
  var wav = new Uint8Array( headerLength + dataLength );
  var view = new DataView( wav.buffer );

  view.setUint32( 0, 1380533830, false ); // RIFF identifier 'RIFF'
  view.setUint32( 4, 36 + dataLength, true ); // file length minus RIFF identifier length and file description length
  view.setUint32( 8, 1463899717, false ); // RIFF type 'WAVE'
  view.setUint32( 12, 1718449184, false ); // format chunk identifier 'fmt '
  view.setUint32( 16, 16, true ); // format chunk length
  view.setUint16( 20, 1, true ); // sample format (raw)
  view.setUint16( 22, this.numberOfChannels, true ); // channel count
  view.setUint32( 24, this.sampleRate, true ); // sample rate
  view.setUint32( 28, this.sampleRate * this.bytesPerSample * this.numberOfChannels, true ); // byte rate (sample rate * block align)
  view.setUint16( 32, this.bytesPerSample * this.numberOfChannels, true ); // block align (channel count * bytes per sample)
  view.setUint16( 34, this.bitDepth, true ); // bits per sample
  view.setUint32( 36, 1684108385, false); // data chunk identifier 'data'
  view.setUint32( 40, dataLength, true ); // data chunk length

  for (var i = 0; i < this.recordedBuffers.length; i++ ) {
    wav.set( this.recordedBuffers[i], i * bufferLength + headerLength );
  }

  self.postMessage( wav, [wav.buffer] );
  self.close();
};