I finally got around to porting my CodeIgniter YouTube API Library to regular PHP. There honestly aren't that many CI dependencies so it was a fairly easy library to port.
I changed how the constructor is setup so it's a little more descriptive when being instantiated. All of the API calls remained the same so you can checkout the CI library for example calls to make. I included some example code on how to use the API. The example files are index.php and authorize.php they demonstrate how to authenticate with YouTube then make calls. Let me know if you have any issues or questions.
The GitHub repos is: https://github.com/jimdoescode/Zendless-PHP-YouTube-API