problem with chunk upload file in plupload and php

Question

I have implemented chunk file upload with plupload documentation, it's work fine in small files. but when uploading big file size like movie, zip, etc. after upload file, the file is shown as some thing like this: file_631c9212682f7

note that upload works up to 100% .

test.php

<!-- File browse input field -->
<div class="form-group">
    <label><b>Select File:</b></label>
    <input type="file" class="form-control" id="fileInput">
</div>

<!-- List the selected files -->
<div id="fileList"></div>

<!-- Upload button -->
<div class="form-group">
    <a id="uploadBtn" href="javascript:;" class="btn btn-success">Upload</a>
</div>


<!-- Progress bar -->
<div class="progress"></div>

<script src="plupload/js/plupload.full.min.js"></script>

<script>
// Define Plupload uploader with configuration options
var uploader = new plupload.Uploader({
    runtimes : 'html5,flash,silverlight,html4',
    browse_button : 'fileInput', // you can pass an id...
    url : 'upload.php',
    flash_swf_url : 'plupload/js/Moxie.swf',
    silverlight_xap_url : 'plupload/js/Moxie.xap',
    multi_selection: false,
    
    filters : {
        max_file_size : '500mb',
        mime_types: [
            {title : "Image files", extensions : "jpg,jpeg,gif,png"},
            {title : "Video files", extensions : "mp4,avi,mpeg,mpg,mov,wmv"},
            {title : "Zip files", extensions : "zip"},
            {title : "Document files", extensions : "pdf,docx,xlsx"}
        ]
    },

    init: {
        PostInit: function() {
            document.getElementById('fileList').innerHTML = '';

            document.getElementById('uploadBtn').onclick = function() {
                if (uploader.files.length < 1) {
                    document.getElementById('statusResponse').innerHTML = '<p style="color:#EA4335;">Please select a file to upload.</p>';
                    return false;
                }else{
                    uploader.start();
                    return false;
                }
            };
        },


        FilesAdded: function(up, files) {
            plupload.each(files, function(file) {
                document.getElementById('fileList').innerHTML += '<div id="' + file.id + '">' + file.name + ' (' + plupload.formatSize(file.size) + ') <b></b></div>';
            });
        },

        UploadProgress: function(up, file) {
            document.getElementById(file.id).getElementsByTagName('b')[0].innerHTML = '<span>' + file.percent + "%</span>";
            document.querySelector(".progress").innerHTML = '<div class="progress-bar" style="width: '+file.percent+'%;">'+file.percent+'%</div>';
        },
        
        FileUploaded: function(up, file, result) {
            var responseData = result.response.replace('"{', '{').replace('}"', '}');
            var objResponse = JSON.parse(responseData);
            document.getElementById('statusResponse').innerHTML = '<p style="color:#198754;">' + objResponse.result.message + '</p>';
        },

        Error: function(up, err) {
            document.getElementById('statusResponse').innerHTML = '<p style="color:#EA4335;">Error #' + err.code + ': ' + err.message + '</p>';
        }
    }
});

// Initialize Plupload uploader
uploader.init();
</script>

upload.php

<?php 
// Make sure file is not cached (as it happens for example on iOS devices) 
header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); 
header("Last-Modified: " . gmdate("D, d M Y H:i:s") . " GMT"); 
header("Cache-Control: no-store, no-cache, must-revalidate"); 
header("Cache-Control: post-check=0, pre-check=0", false); 
header("Pragma: no-cache"); 
 
// Settings 
$targetDir = 'uploads'; 
$cleanupTargetDir = true; // Remove old files 
$maxFileAge = 5 * 3600; // Temp file age in seconds 
 
 
// Create target dir 
if (!file_exists($targetDir)) { 
    @mkdir($targetDir); 
} 
 
// Get a file name 
if (isset($_REQUEST["name"])) { 
    $fileName = $_REQUEST["name"]; 
} elseif (!empty($_FILES)) { 
    $fileName = $_FILES["file"]["name"]; 
} else { 
    $fileName = uniqid("file_"); 
} 
 
$filePath = $targetDir . DIRECTORY_SEPARATOR . $fileName; 
 
// Chunking might be enabled 
$chunk = isset($_REQUEST["chunk"]) ? intval($_REQUEST["chunk"]) : 0; 
$chunks = isset($_REQUEST["chunks"]) ? intval($_REQUEST["chunks"]) : 0; 
 
 
// Remove old temp files     
if ($cleanupTargetDir) { 
    if (!is_dir($targetDir) || !$dir = opendir($targetDir)) { 
        die('{"jsonrpc" : "2.0", "error" : {"code": 100, "message": "Failed to open temp directory."}, "id" : "id"}'); 
    } 
 
    while (($file = readdir($dir)) !== false) { 
        $tmpfilePath = $targetDir . DIRECTORY_SEPARATOR . $file; 
 
        // If temp file is current file proceed to the next 
        if ($tmpfilePath == "{$filePath}.part") { 
            continue; 
        } 
 
        // Remove temp file if it is older than the max age and is not the current file 
        if (preg_match('/\.part$/', $file) && (filemtime($tmpfilePath) < time() - $maxFileAge)) { 
            @unlink($tmpfilePath); 
        } 
    } 
    closedir($dir); 
}     
 
 
// Open temp file 
if (!$out = @fopen("{$filePath}.part", $chunks ? "ab" : "wb")) { 
    die('{"jsonrpc" : "2.0", "error" : {"code": 102, "message": "Failed to open output stream."}, "id" : "id"}'); 
} 
 
if (!empty($_FILES)) { 
    if ($_FILES["file"]["error"] || !is_uploaded_file($_FILES["file"]["tmp_name"])) { 
        die('{"jsonrpc" : "2.0", "error" : {"code": 103, "message": "Failed to move uploaded file."}, "id" : "id"}'); 
    } 
 
    // Read binary input stream and append it to temp file 
    if (!$in = @fopen($_FILES["file"]["tmp_name"], "rb")) { 
        die('{"jsonrpc" : "2.0", "error" : {"code": 101, "message": "Failed to open input stream."}, "id" : "id"}'); 
    } 
} else {     
    if (!$in = @fopen("php://input", "rb")) { 
        die('{"jsonrpc" : "2.0", "error" : {"code": 101, "message": "Failed to open input stream."}, "id" : "id"}'); 
    } 
} 
 
while ($buff = fread($in, 4096)) { 
    fwrite($out, $buff); 
} 
 
@fclose($out); 
@fclose($in); 
 
// Check if file has been uploaded 
if (!$chunks || $chunk == $chunks - 1) { 
    // Strip the temp .part suffix off  
    rename("{$filePath}.part", $filePath); 
} 
 
// Return Success JSON-RPC response 
die('{"jsonrpc" : "2.0", "result" : {"status": 200, "message": "The file has been uploaded successfully!"}}');

I think in the end of uploading, the chunks doesn't concatinate to each other to make the final original file. I never understand the reason of this issue, please help me to solve this problem.

in the end, excuse me because of my weak english language.