@Damien-Rambacher All of the video are like that. If you're in a major city with super fast fibre broadband it probably won't be an issue, but over here in the UK it is for me too. It's because they're uploading their videos at the highest quality with the compression not suitable for streaming I'm guessing. Either that or it's the load on whatever server they're using is the issue. Obviously we're spoilt with sites like YouTube that invest billions in their servers and compression are able to deliver 1080p or even 4k video without hardly any buffering.
Try different browsers. For me, Chrome streams them better than Safari on my Mac.
Ace