I went into the Apple Store a while back to see which Mac fit my needs. I thought that having heard about 4K videos being released on YT, it might be worth trying some out on the Retina Macs. Breathless was the result - simply stunning. Now, I went to a third party store a while back and they also had some RMBP's and I tried to do the same...however it said there was a missing plug-in and there wasn't even an option to view in 4K (on the same video I played in the Apple Store)..just 720p. I'm just wanting to inquire about this in advance, so that when I get my Mac, I'm all set to view such videos. Trying to view them on my Windows laptop as of now, is painful. It won't even load. If anybody has any idea what plug in it may be missing, that'd be fantastic - that way I can download it once I get my Mac. Thanks!