The YouTube Data API allows client applications to retrieve and update YouTube content in the form of Google Data API feeds. Your client application can use the YouTube Data API to fetch video feeds, comments, responses, and playlists, as well as query for videos that match particular criteria. You can also use the API to make authenticated requests to modify this information and to upload new video content to the site.
In addition to providing some background on the capabilities of the YouTube Data API, this document provides examples for interacting with the API using the PHP client library http://framework.zend.com/downloads/latest You can download the client library as a standalone release (distributed by Zend) or as part of the Zend Framework. If you need help setting up the PHP client library, the Getting Started Guide is the place to look.