Clean the name for a file and avoid rewrite files when they are being uploaded to server. Rename it by adding a sequential number at the end of name, before extension.

clean-file-name-dash.php

<?php

// Just keep letters and numbers. 
// Replace everything else with dash, even spaces.
//------------------------------------------------------------------------------

$path = dirname(__FILE__);
$file = 'Dos elefantes.mp4'; // Already exists in server

$filename   = substr($file, 0, strrpos($file, '.'));
$extension  = substr($file, strrpos($file, '.'));
$filename   = strtolower(preg_replace('/[^[:alnum:]]/', '-', $filename)) . $extension;

while(is_file($path . $filename)) {
    $filename = preg_replace_callback(
        '/(?:(?:-([\d]+))?(\.[^.]+))?$/',
        function ($match) {
            $index  = isset($match[1]) ? intval($match[1]) + 1 : 1;
            $ext    = isset($match[2]) ? $match[2] : '';

            return '-' . str_pad($index, 2, '0', STR_PAD_LEFT) . $ext;
        }, 
        $filename, 1
    );
}

// Result
echo $filename; // dos-elefantes-01.mp4

// If you try upload the same file
echo $filename; // dos-elefantes-02.mp4

clean-file-name.php

<?php

// Just keep letters, numbers and spaces. 
// Remove everything else.
//------------------------------------------------------------------------------

$path = dirname(__FILE__);
$file = 'Dos elefantes.mp4'; // Already exists in server

$filename   = substr($file, 0, strrpos($file, '.'));
$extension  = substr($file, strrpos($file, '.'));
$filename   = preg_replace('/[^[:alnum:] ]/', '', $filename) . $extension;

while(is_file($path . $filename)) {
    $filename = preg_replace_callback(
        '/(?:(?: \(([\d]+)\))?(\.[^.]+))?$/',
        function ($match) {
            $index  = isset($match[1]) ? intval($match[1]) + 1 : 1;
            $ext    = isset($match[2]) ? $match[2] : '';

            return ' ('.$index.')' . $ext;
        }, 
        $filename, 1
    );
}

// Result
echo $filename; // Dos elefantes (1).mp4

// If you try upload the same file again, will going to be renamed again
echo $filename; // Dos elefantes (2).mp4