使用JQuery和PHP进行Ajax上传

我在使用Jquery和PHP上传Ajax时遇到问题。尽管有很多关于同一主题的stackoverflow帖子，但我找不到与我的情况相符的帖子。

HTML：

<form action="uploadrecord.php" id="upload_record_form" method="post" enctype="multipart/form-data">
               <div id="upload_record_form_result"></div>
                <ul>
                    <li><input type="file" name="uploadrecord" id="uploadrecord"/></li>
                </ul>
                 <progress></progress>
            </form>

        </div>

Javascript：

 $('#uploadrecord').live('change', function(event) {

        var formData = new FormData($('#upload_record_form')[0]);

        $.ajax({
            url: $('#upload_record_form').attr('action'),
            type: 'POST',
            enctype: 'multipart/form-data',
            xhr: function() {  
                myXhr = $.ajaxSettings.xhr();
                if (myXhr.upload) { 
                    myXhr.upload.addEventListener('progress', progressHandlingFunction, false); 
                }
                return myXhr;
            },

            success: completeHandler = function(data) {
                $('#upload_record_form_result').html(data);
            },
            error: errorHandler = function() {
                alert("Failure");
            },
            data: formData,
            cache: false,
            contentType: false,
            processData: false
        }, 'json');


    });

的PHP

<?php
if (isset($_FILES['uploadrecord'])) {
    if ((!empty($_FILES["uploadrecord"])) && ($_FILES['uploadrecord']['error'] == 0)) {

        $filename = basename($_FILES['uploadrecord']['name']);
        $ext = substr($filename, strrpos($filename, '.') + 1);

        $types = array(
            'video/mp4', 'video/3gpp', 'video/divx', 'video/flv', 'video/mpeg', 'video/mpeg-2', 'video/mpeg4', 'video/mpeg4'
        );

        $type = $_FILES['uploadrecord']['type'];
        if (in_array($type, $types) && $_FILES["uploadrecord"]["size"] < 20000000) {

            $new = sha1(date('Y/m/d H:i:s'));
            $newname = dirname(__FILE__) . '/records/' . $new . '.' . $ext;

            if ((move_uploaded_file($_FILES['uploadrecord']['tmp_name'], $newname))) {
                echo 'done';
            } else {
                echo 'failed 1';
            }
        }
   } else {
       echo 'failed 2';
    }
} else {
    echo 'Upload failed 3';
}

当我尝试前面的代码并上载记录文件时，它显示“失败2”，这意味着“错误”代码不同于0。

当我var_dump数组$ _FILES ['uploadrecord'] ...这就是我得到的：

array (size=5)
  'name' => string 'Nao Robot.flv' (length=13)
  'type' => string '' (length=0)
  'tmp_name' => string '' (length=0)
  'error' => int 1
  'size' => int 0

我不知道为什么'tmp_name'和type设置为空字符串，以及为什么将大小设置为0。

到底出什么问题了？是从客户端还是服务器端脚本编写的？

提前致谢