This app was mentioned in 1 comment, with an average of 1.00 upvote
To be fair, I don't watch a lot of 60fps content on YouTube. It's mostly just supercar vloggers and then fails videos with a Mrs, so I'm hardly the best example (particularly since most don't upload anything in 60fps anyway), so maybe I don't get anything at 60fps?
I also don't use the XB1 app so much as it's just a "player" with everything being sent through my phone.
As for that app, just Google "MyTube" and you'll see it.
Edit: added the app link.