4K and 8K youtube.com tests

https://www.youtube.com/playlist?list=PLIaKMO-GyZCww7ioiBMmHFIrgzsA1qCcu

전환 버튼 표시 안함

https://www.youtube.com/watch?v=6k7a8bw451M

https://www.youtube.com/watch?v=LXb3EKWsInQ

전환 버튼 표시 함.

https://www.youtube.com/watch?v=N1-Jmq7BLFE