First I would like to apologize for my stupidity…

I need to provide a download of large videofiles from a webpage.
The files are between 4 and 20 gb.

Question: What is the right way to enable such a download?

I tried some ways but the download always aborted or did not work

First try was this because I have used it for some smaller files in the past – but in this case the download stopped at 1 GB

header("Content-Type: $type");
header("Content-Disposition: attachment; filename="$fileName"");
readfile($dir.$file);

I tried also to download it chunk by chunk. The browser started the download correctly but crashed after a short time.

$chunksize = 5 * (1024 * 1024); //5 MB (= 5 242 880 bytes) per one chunk of file.

    if(file_exists($filename))
    {
        set_time_limit(10800);

        $size = intval(sprintf("%u", filesize($filename)));

        header('Content-Type: application/octet-stream');
        header('Content-Transfer-Encoding: binary');
        header('Content-Length: '.$size);
        header('Content-Disposition: attachment;filename="'.basename($filename).'"');

        if($size > $chunksize)
        {
            $handle = fopen($filename, 'rb');

            while (!feof($handle))
            {
                print(@fread($handle, $chunksize));

                ob_flush();
                flush();
            }

            fclose($handle);
        }
        else readfile($filename);

        exit;
    }
    else echo 'File "'.$filename.'" does not exist!';*/

Last try was X-Sendfile, but I think the webhosting Server does not support it, because it does not work?

if (file_exists($fileonserver))
    {
        // send the right headers
        header('Cache-Control: no-store, no-cache, must-revalidate, max-age=0');
        header('Cache-Control: post-check=0, pre-check=0', false);
        header('Pragma: no-cache');
        header('Content-type: ' . $type);
        header('Content-Length: ' . filesize($fileonserver));

        header('X-Sendfile: ' . $fileonserver);
        //exit;
    }
    else
    {
        die('File loading failed.');
    }