Well it depends maybe you can add it via a plugin depending on the script/CMS your using, or if your interested in creating it yourself, then you would need moderate PHP/MySQL experience, and assuming you had this then you'd create a ratings table, with an articleid linking to the article and columns counting the amount of ratings. You then display the stars on each article, you could use some JS or just use plain CSS, and when somebody clicks a star it updates the table and adds 1 to the star voted for in relation to the article ID. A last alternative to this would be just to find a rating script, but you'd have to fiddle with it anyway to get it to work with whatever you are using.
Since you mentioned your video website is in php, it will require some experience to add requested functionality, otherwise you can broke the code. It is likely that you will also need to modify your database structure. If you really need help, I can do this for you for reasonable compensation