How force download mp4 file

Hi
I have 10 video files with mp4 format
I download this files from my php script
My code is :

PHP Code:

header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: attachment; filename='.basename($filename).'?id='.time());
header('Content-Transfer-Encoding: binary');
header('Expires: 0');
header('Cache-Control: must-revalidate, post-check=0, pre-check=0');
header('Pragma: public');
header('Content-Length: ' . filesize($filename));
readfile($filename); 


But speed is low when user try to download
and when i use redirect(base_url().$filename); speed is good and user can watch video speedly

M goal from this way is user cannnot download video and have to watch it with my php script file

Thanks