How to slice an AudioBuffer

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);
}