ini_set('memory_limit','128M');

• Or add the following line to .htaccess

php_value memory_limit 128M

First solution is the best option, since the other 2 might not work due to security settings.

The PHP way *ultimate solution*

This solution we don’t need to increase PHP memory limit.
This will read 8kb of file and push it to the client AND not the full file!

header ("Content-type: octet/stream");
header ("Content-disposition: attachment; filename=".$filename.".mp4;");
header("Content-Length: ".filesize($myFile));
ob_clean();
$handle=fopen($_REQUEST['file'], 'rb');
while (!feof($handle))
{ 
    echo fread($handle, 8192);
    flush();
}
fclose($handle);

The .htaccess way

The normal file type for MP4 is video/mp4.
This way the browser will try to play it and won’t download it.

We can force .htaccess to change it and force the download.

Lets say that we want to force the download when the URL has a ?dl.

RewriteCond %{QUERY_STRING} dl
RewriteRule .*\.mp4 - [T=application/octet-stream]

This way .htaccess www.domain.com/video.mp4?dl and change the file type to application/octet-stream – the one that forces the download.