diff --git a/src/Zend/Exception.php b/src/Zend/Exception.php
new file mode 100644
index 0000000..a439b5f
--- /dev/null
+++ b/src/Zend/Exception.php
@@ -0,0 +1,96 @@
+<?php
+/**
+ * Zend Framework
+ *
+ * LICENSE
+ *
+ * This source file is subject to the new BSD license that is bundled
+ * with this package in the file LICENSE.txt.
+ * It is also available through the world-wide-web at this URL:
+ * http://framework.zend.com/license/new-bsd
+ * If you did not receive a copy of the license and are unable to
+ * obtain it through the world-wide-web, please send an email
+ * to license@zend.com so we can send you a copy immediately.
+ *
+ * @category   Zend
+ * @package    Zend
+ * @copyright  Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)
+ * @license    http://framework.zend.com/license/new-bsd     New BSD License
+ * @version    $Id: Exception.php 23483 2010-12-10 03:40:01Z mjh_ca $
+ */
+
+/**
+* @category   Zend
+* @package    Zend
+* @copyright  Copyright (c) 2005-2010 Zend Technologies USA Inc. (http://www.zend.com)
+* @license    http://framework.zend.com/license/new-bsd     New BSD License
+*/
+class Zend_Exception extends Exception
+{
+    /**
+     * @var null|Exception
+     */
+    private $_previous = null;
+
+    /**
+     * Construct the exception
+     *
+     * @param  string $msg
+     * @param  int $code
+     * @param  Exception $previous
+     * @return void
+     */
+    public function __construct($msg = '', $code = 0, Exception $previous = null)
+    {
+        if (version_compare(PHP_VERSION, '5.3.0', '<')) {
+            parent::__construct($msg, (int) $code);
+            $this->_previous = $previous;
+        } else {
+            parent::__construct($msg, (int) $code, $previous);
+        }
+    }
+
+    /**
+     * Overloading
+     *
+     * For PHP < 5.3.0, provides access to the getPrevious() method.
+     *
+     * @param  string $method
+     * @param  array $args
+     * @return mixed
+     */
+    public function __call($method, array $args)
+    {
+        if ('getprevious' == strtolower($method)) {
+            return $this->_getPrevious();
+        }
+        return null;
+    }
+
+    /**
+     * String representation of the exception
+     *
+     * @return string
+     */
+    public function __toString()
+    {
+        if (version_compare(PHP_VERSION, '5.3.0', '<')) {
+            if (null !== ($e = $this->getPrevious())) {
+                return $e->__toString()
+                       . "\n\nNext "
+                       . parent::__toString();
+            }
+        }
+        return parent::__toString();
+    }
+
+    /**
+     * Returns previous Exception
+     *
+     * @return Exception|null
+     */
+    protected function _getPrevious()
+    {
+        return $this->_previous;
+    }
+}
diff --git a/src/Zend/Media/Iso14496/Box/Tfra.php b/src/Zend/Media/Iso14496/Box/Tfra.php
index 4e291fa..1532600 100644
--- a/src/Zend/Media/Iso14496/Box/Tfra.php
+++ b/src/Zend/Media/Iso14496/Box/Tfra.php
@@ -37,7 +37,7 @@ require_once 'Zend/Media/Iso14496/FullBox.php';
 /**#@-*/
 
 /**
- * The <i>Track Fragment Random Access Box<i> provides entries that contains the location and the presentation time of
+ * The <i>Track Fragment Random Access Box</i> provides entries that contains the location and the presentation time of
  * the random accessible sample. It indicates that the sample in the entry can be random accessed. Note that not every
  * random accessible sample in the track needs to be listed in the table.
  *
@@ -288,6 +288,10 @@ final class Zend_Media_Iso14496_Box_Tfra extends Zend_Media_Iso14496_FullBox
         }
     }
 
+    /**
+     * Returns the length sizes based on maximum numbers for each type of integer.
+     * @return integer Returns the length sizes based on maximum numbers for each type of integer.
+     */
     private function _getLengthSizes()
     {
         $maxTrafNum = $maxTrunNum = $maxSampleNum = 0;
@@ -309,6 +313,12 @@ final class Zend_Media_Iso14496_Box_Tfra extends Zend_Media_Iso14496_FullBox
         );
     }
 
+    /**
+     * Returns the length size based on the given integer.
+     *
+     * @param integer $integer The integer to determine the length size from.
+     * @return Returns the length size of the given integer.
+     */
     private function _getLengthSizeFromInteger($integer)
     {
         if ($integer <= 0xff) {