4K video on 6S
Hello I have a 6S and 4K is supported, but while trying to watch YouTube videos in 4K, the highest resolution is 720p. I am using the YouTube app.
iPhone 6s, iOS 9.2, Andrew's 6S
4K video on the iPhone 6s, means that when you shoot your own video clips on the phone, you can shoot them in 4K.
It is not referring to YouTube and play back. YouTube videos can only be watched in what is supported on YouTube and how they were made by the posted. Yes, some YouTube videos have HD options available, but not all and if they are not available then you can only playback what is there.
As I said before - the 4K option is for shooting your own video clips and has nothing to do with YouTube.