click the pencil to edit an item and put in the ID of the YouTube video (not the entire URL)
I'm sure you will figure out the right regexp to extract the ID so you don't have to rely on the user to extract it

I arrived at this:
/(?<=(?:v|i)=)[a-zA-Z0-9-]+(?=&)|(?<=(?:v|i)\/)[^&\n]+|(?<=embed\/)[^"&\n]+|(?<=(?:v|i)=)[^&\n]+|(?<=youtu.be\/)[^&\n]+/
Testing:
$urls = array(
'',
'youtube.com/v/dQw4w9WgXcQ',
'youtube.com/vi/dQw4w9WgXcQ',
'youtube.com/?v=dQw4w9WgXcQ',
'youtube.com/?vi=dQw4w9WgXcQ',
'youtube.com/watch?v=dQw4w9WgXcQ',
'youtube.com/watch?vi=dQw4w9WgXcQ',
'youtu.be/dQw4w9WgXcQ',
);
foreach ($urls as $url) {
preg_match('/(?<=(?:v|i)=)[a-zA-Z0-9-]+(?=&)|(?<=(?:v|i)\/)[^&\n]+|(?<=embed\/)[^"&\n]+|(?<=(?:v|i)=)[^&\n]+|(?<=youtu.be\/)[^&\n]+/', $url, $matches);
print_r($matches);
}
Works for all of 'em:
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)
Array
(
[0] => dQw4w9WgXcQ
)