How do I check if a video exists on YouTube, using PHP?

Question

How do I check if a video exists on YouTube, using PHP?

Answer 1

What about using Youtube's API?
After all, that would mean using some official, which is less likely to change than going with parsing some HTML page.

For more information: YouTube APIs and Tools - Developer's Guide: PHP

The Retrieving a specific video entry seems quite interesting: if you send a request to an URL like this one:

http://gdata.youtube.com/feeds/api/videos/videoID

(replacing "videoID" by the ID of the video, of course – "GeppLPQtihA" in your example), you'll get some ATOM feed if the video is valid; and "Invalid id" if it's not

And, I insist: this way, you rely on a documented API, and not on some kind of behavior that exists today, but is not guaranteed.