1
The structure of the site is as follows:
index.html:
<script src="http://ajax.googleapis.com/ajax/libs/jquery/1.11.1/jquery.min.js"></script>
    <script>
       // verifica se a página foi carregada para evitar aplicar os códigos antes de ter algum elemento não carregado...
        $(document).ready(function(){
            $(".ajax").on("click", function(e){
                e.preventDefault(); //eliminamos o evento
                var path = $(this).attr('href'); //Pegamos o caminho
                $("#main").empty();
                $("#main").load(path); //Faz uma requisição http para o servidor. //carrega a página (o path) passada como parâmetro... 
            });
        });
</script>
<body>
    <nav>
            <ul>
                <li><a href="./contato.html" class="ajax" data-title="Meu site - Contato">Contato</a></li>
                <li><a href="./sobre.html" class="ajax" data-title="Meu site - Sobre">Sobre</a></li>
                <li><a href="./upload.php" class="ajax" data-title="Meu site - upload">upload</a></li>
            </ul>
    </nav>
   <article id='main'> <!-- #main será atualizado consoante a navegação que o utilizador fizer via Ajax... -->         
      <!-- Home.html -->  
   </article>
</body>
upload.php:
<?php
include 'functions.php';
include 'db_connect.php';
$requestMethod = isset($_SERVER['REQUEST_METHOD']) ? $_SERVER['REQUEST_METHOD'] : null;
$submit = isset($_POST['submit']) ? $_POST['submit'] : null;
//Pregunta si está llegando una petición por POST, lo que significa que el usuario envió (submit) el formulario.
if ($requestMethod === 'POST' && $submit === 'Upload'){
    $file_audio = $_FILES["input_audio"]; 
    $file_cover = $_FILES["input_cover"]; 
    $errors_file_audio = valida_file_audio($file_audio); 
    $errors_file_cover = valida_file_cover($file_cover);
     if (empty($errors_file_audio) && empty($errors_file_cover)){
            $status  =  save_files($file_audio, $file_cover, $mysqli);
             if (is_array($status) && !empty($status)){
                foreach ($status as $item){
                    echo "<label> <p style='color:red;'>" . $item . "<br />" . "</p></label>";
                }
            }else{
                    //echo"<label> <p style='color:green;'> Upload realizado com sucesso!</p> </label>";
                 } 
    }
}
?>
<!-- Validar Campos com JavaScript e JQuery -->
<script src="jquery-1.6.2.js" type="text/javascript"></script>
<script src="jquery.validate.js" type="text/javascript"></script>
<script src="validar.js" type="text/javascript"></script>
<!--CSS para configurar as mensagens de erro (js e Jquery) -->
<style type="text/css">
/* Estilizar os alertas */
label.error{
padding-left: 5px;
color: red;
font-weight: bold;
}
</style>
<div class='upload'>
        <h1>Upload</h1>
            <?php
            $sucesso = isset($_GET['sucesso']) ? $_GET['sucesso'] : null;
            if ($sucesso == 'sdfgjhksladtfJH456') {
                echo"<label> <p style='color:green;'> Upload realizado com sucesso!</p> </label>";
            }
            ?>
            <form id="form_Upload" enctype="multipart/form-data" action="upload.php"  method="POST">
                        <label for="audio">MP3:</label><br />
                        <input type="file" name="audio" id="audio" size="45" />    
                        <?php
                            $errors_file_audio = isset($errors_file_audio) ?  $errors_file_audio : null;
                                if (is_array($errors_file_audio)){
                                    foreach ($errors_file_audio as $item){
                                         echo " <label> <p style='color:red;'>" . $item . "<br />" . "</p>  </label>";
                                    }
                                }
                        ?>
                        <br /><br />
                        <label for="cover">Cover:</label><br />
                        <input type="file" name="cover" id="cover" size="45" />
                        <?php
                             $errors_file_cover = isset($errors_file_cover) ?  $errors_file_cover : null;
                                if (is_array($errors_file_cover)){
                                    foreach ($errors_file_cover as $item){
                                         echo "<label> <p style='color:red;'>" . $item . "<br />" . "</p>  </label>";
                                    }
                                }              
                        ?>
                        <br /><br />
                        <input type="submit" name="submit" value="Upload" />
                     </form>
</div>   
That is, I have a main page (index.html) that "loads", via Ajax, for the tag <article></article> the selected page....  
The idea is to submit the form, without being redirected by the action="upload.php" attribute of the tag <form></form>. That is, stay at index.html and keep upload.php inside the tag <article></article> even after uploading the files. 
What is the ideal solution for this case?
Yes, how do I do that in practical terms?
– user12141
At a glance at this article, he uses Formdata to submit the
formwithinput fileusing ajax. http://portfolio.planetjon.ca/2014/01/26/submit-file-input-via-ajax-jquery-easy-way/– Wakim
Wakim, I graduate your availability.
– user12141