Method 1
$file = 'video.mp4';
$extension = preg_replace('/^.*./', '', $file);
Method 2
$file = 'video.mp4';
$extension = explode('.', $file);
$extension = end($extension);
Method 3
$file = 'video.mp4';
$extension = explode('.', $file);
$extension = array_pop($extension);
Method 4
$file = 'video.mp4';
$extension = pathinfo($file, PATHINFO_EXTENSION);
Method 5
$file = 'video.mp4';
$file_info = pathinfo($file);
$extension = $file_info['extension'];
// $file_info is an Array which will output something similar to:
Array
(
[dirname] => .
[basename] => video.mp4
[extension] => mp4
[filename] => video
)
Method 6
$file = 'video.mp4';
$extension = substr(strrchr($file, '.'), 1);