Custom view format, parse a text value I think this is a pretty easy thing to do once you figure it out once, but I'm struggling to do the following:

I have a content type called YouTube video. It accepts a text field "URL" that is the full video URL (or alternatively just the ending video ID)

I want the displayed content to be an embedded video. How can I set the default embed code and then have a variable to swap for the ID? 

Edit: Been poking all day, still can't figure this one out. I'm from a Wordpress background and this would be a simple ~3 minute addition to functions.php. Can someone point me in the right direction?
If you want the fields approach, try looking at the module http://drupal.org/project/emfield
If you want to do it yourself in code, there are different approaches, the most basic one being adding a node template for your content type and adding your embed code there. Look at drupal.org for basic information about addding templates.