$local_file = 'file.zip';
$download_file = 'name.zip';
 
// set the download rate limit (=> 20,5 kb/s)
$download_rate = 20.5;
if(file_exists($local_file) && is_file($local_file))
{
    header('Cache-control: private');
    header('Content-Type: application/octet-stream');
    header('Content-Length: '.filesize($local_file));
    header('Content-Disposition: filename='.$download_file);
 
    flush();
    $file = fopen($local_file, "r");
    while(!feof($file))
    {
        // send the current file part to the browser
        print fread($file, round($download_rate * 1024));
        // flush the content to the browser
        flush();
        // sleep one second
        sleep(1);
    }
    fclose($file);}
else {
    die('Error: The file '.$local_file.' does not exist!');
}

 
 <?php
/* aqui el numero de kilobytes de descarga (ej. 10.20 Kb/s) */
$download_rate = 10.20;
 
$download_file = 'download-file.zip';  
$target_file = 'target-file.zip';
 
if(file_exists($download_file)){
    /* headers */
    header('Last-Modified: '.gmdate('D, d M Y H:i:s').' GMT');
    header('Cache-control: private');
    header('Content-Type: application/octet-stream');
    header('Content-Length: '.filesize($download_file));
    header('Content-Disposition: filename='.$target_file);
 
    /* flush */
    flush();
 
    /* abrir archivo */
    $fh = @fopen($download_file, 'r');
    while(!feof($fh)){
        /* mandamos parte del archivo */
        print fread($fh, round($download_rate * 1024));
        /* flush del contenido al navegador */
        flush();
        /* sleep de 1 segundo */
        sleep(1);
    }
    /* cerrar archivo */
    @fclose($fh);
}else{
    die('Error: '.$download_file.' no existe!');
}
?>