YouTube introduced videos that play at 60 frames per second last year and ones viewable in 4K resolution in February. Now, the website is starting to experiment with videos that are both silky smooth and ultra high-def. TechCrunch has spotted a low-key, semi-secret playlist comprised of only six videos that you can choose to play at 60 fps in 4K resolution -- just toggle the settings switch to see the option. You'll have to load YouTube on Chrome to see the 2160p60 4K setting under Quality. Plus, you'll need a device capable of displaying ultra HD (3840 × 2160 resolution) to enjoy the feature's benefits. Trust us when we say it's not worth the buffering time if your computer or TV isn't designed to handle 4K: the videos will look worse. We've embedded all six files below the fold, but feel free to visit the playlist itself to watch them all continuously.