Not necessarily. the TV licence site says " if you are watching a TV programme live on YouTube, you need to be covered by a TV Licence. A licence is not required to view user generated content, clips and videos on YouTube. This includes live streamed content that is not part of a television broadcast."I'll start by saying I'm in favour of the licence fee and think it's excellent VFM.
That said, I hadn't realised the full extent of the requirements for the licence. Let me get this straight, if I'm watching YouTube videos through a smart TV I'd need a licence? That does seem pretty bonkers.