Safari 10.0 on MacOS Sierra unable to play 1080p60 videos on YouTube anymore?

Hi! I upgraded to MacOS Sierra on my Mac Mini today and I noticed that Safari 10.0 is unable to play 1080p60fps videos on YouTube smoothly, I have to move it down to 720p60fps to watch if in safari. It's not because my Mac Mini is from 2011 or anything like that, because the videos play just fine in Mozilla Firefox and Google Chrome. Is there anything to this? Thanks.