I am using YTPlayerView iOS class which is provided by Youtube and you can check it here.
The problem is the following: on iPhone the video automatically starts in full screen while on iPad it doesn't, and I need to start it in full screen by default.
For anyone who is facing this problem, I solved it by dropping this class and using XCDYoutubeKit, it solved my issue but I had to drop the separate UI where I used my player.
https://github.com/0xced/XCDYouTubeKit
It's also available through cocoapods