title: PHP: How to know if link is a valid youtube link?
body: <p>Here are examples.</p>
  
  <pre><code>www.youtube.com,
  http://www.youtube.com/,
  http://www.youtube.com/watch?v=YoB8t0B4jx4
  </code></pre>
  
  <p>I don't care if it has video or just youtube url but just valid url.
  What I want to do is when i know that it is a valid youtube url i will check if it has video ID.
  If it has ID i will add iframe for video and if has no it will be just plane text.
  I just want to know if a link is a valid youtube weather it has http or not, weather it has
  ID or not.
  Im not good at regular expression now and i need the code now pls help thanks in advance</p>