audiobuffer-slice/audiobuffer-slice.js

Slice out a portion of an AudioBuffer.

(function(root) {
  'use strict';

  var audioContext = new (window.AudioContext || window.webkitAudioContext);

  function audioBufferSlice(buffer, begin, end, callback) {
    if (!(this instanceof audioBufferSlice)) {
      return new audioBufferSlice(buffer, begin, end, callback);
    }

    var error = null;

    var duration = buffer.duration;
    var channels = buffer.numberOfChannels;
    var rate = buffer.sampleRate;

    if (typeof end === 'function') {
      callback = end;
      end = duration;
    }

    // milliseconds to seconds
    begin = begin/1000;
    end = end/1000;

    if (begin < 0) {
      error = new RangeError('begin time must be greater than 0');
    }

    if (end > duration) {
      error = new RangeError('end time must be less than or equal to ' + duration);
    }

    if (typeof callback !== 'function') {
      error = new TypeError('callback must be a function');
    }

    var startOffset = rate * begin;
    var endOffset = rate * end;
    var frameCount = endOffset - startOffset;
    var newArrayBuffer;

    try {
      newArrayBuffer = audioContext.createBuffer(channels, endOffset - startOffset, rate);
      var anotherArray = new Float32Array(frameCount);
      var offset = 0;

      for (var channel = 0; channel < channels; channel++) {
        buffer.copyFromChannel(anotherArray, channel, startOffset);
        newArrayBuffer.copyToChannel(anotherArray, channel, offset);
      }
    } catch(e) {
      error = e;
    }

    callback(error, newArrayBuffer);
  }

  if (typeof exports !== 'undefined') {
    if (typeof module !== 'undefined' && module.exports) {
      exports = module.exports = audioBufferSlice;
    }
    exports.audioBufferSlice = audioBufferSlice;
  } else if (typeof define === 'function' && define.amd) {
    define([], function() {
      return audioBufferSlice;
    });
  } else {
    root.audioBufferSlice = audioBufferSlice;
  }
})(this);