How to get all YouTube iframe from HTML using regex

I want to get all YouTube iframe using regex and want to add specific tag to each record found.

For example <youtube-frame></youtube-frame> to iframe begeing and end.

Needed output:

<youtube-frame><iframe width="560" height="315" src="https://www.youtube.com/embed/vakfMRyjulw" frameborder="0" allowfullscreen></iframe></youtube-frame>

<youtube-frame><iframe width="560" height="315" src="https://www.youtube.com/embed/aDGWMlKPKDs" frameborder="0" allowfullscreen></iframe></youtube-frame>

My Code

$embed = '
<iframe width="560" height="315" src="https://www.youtube.com/embed/vakfMRyjulw" frameborder="0" allowfullscreen></iframe>

<iframe width="600" height="350" src="http://ift.tt/1Zcox1w" frameborder="0" allowfullscreen scrolling="no"></iframe>

<iframe width="560" height="315" src="https://www.youtube.com/embed/aDGWMlKPKDs" frameborder="0" allowfullscreen></iframe>

<iframe width="600" height="350" src="http://ift.tt/1X8oHs5" frameborder="0" allowfullscreen scrolling="no"></iframe>

<iframe width="600" height="350" src="http://ift.tt/1X8oHs5" frameborder="0" allowfullscreen scrolling="no"></iframe>
';

What I have tried?

$pattern = '/<iframe\.*src=\"//youtube"\.*/';
$iframeSrc = preg_match($pattern, $embed, $matches);
var_dump($iframeSrc);

via Chebli Mohamed