下载速度限制脚本不起作用

Question

我找到了一个允许限制文件下载速度的脚本here。

// The file that will be sent to the user
$your_file = 'file.zip';

// Rename the file name
$new_file = 'new-filename.zip';

// Set the download speed limit (70 kb/s)
$download_speed = 70;

if(file_exists($myl_file) && is_file($my_file)) {

    // Headers
    header('Cache-control: private');
    header('Content-Type: application/octet-stream');
    header('Content-Length: '.filesize($my_file));
    header('Content-Disposition: filename='.$new_file);

    // Flush the content
    flush();

    // File stream
    $file = fopen($my_file, "r");

    while (!feof($file)) {

        // Send the current part of the file to the browser
        echo fread($file, round($download_speed* 1024));

        // Flush the content to the browser
        flush();

        // Sleep one second
        sleep(1);
    }

    // Close file stream
    fclose($file);

}
else {
    die('Error: The file '.$my_file.' does not exist!');
}

问题是速度限制不起作用（但我可以下载文件）当我更改$ download_speed值时，我总是在1500-2000 kb / s之间。我在wamp和webserver上测试它但不可能使它工作。有任何想法吗？谢谢你。