Personally, I prefer Ruby to PHP. But:

If the point is to build the video hosting project, and you are productive using PHP, then that's probably the best option.

If the point is to increase the breadth of your development skills while building the video hosting project, choosing a new language like Ruby might make sense.

If you've identified a specific technical challenge in what you want to do that makes PHP problematic, investigating alternatives (including different languages, though that's probably not the first thing to look at) for that particular problem also makes sense.