UserAgent: Mozilla/5.0 (Windows NT 10.0; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36

Example URL:
https://www.youtube.com/watch?v=7mQRDEdJ6Ds

Steps to reproduce the problem:
1. Open a youtube video with 4K
2. Set the quality to 2160p (4K)
3. Open Task Manager
3. Notice the stutter in the video. Task Manager shows 100% CPU usage

Tested on Lenovo Flex 3 (Intel Core i5-6200U CPU/Intel HD 520 GPU) and Acer C720 (Intel Core i3-4005U CPU/Intel HD 4400 GPU). Both have the same problem.

The same issue happens on both Windows 10 and Linux Mint 17. Both OS's were run on the Flex 3 and the Acer C720 to test the problem.

What is the expected behavior?
The video plays back smoothly

What went wrong?
In Chrome with the HTML5 player, Youtube gets 100% CPU Usage playing 4K video and the video buffers and stutters every 3 seconds.

Did this work before? N/A 

Is it a problem with Flash or HTML5? HTML5

Does this work in other browsers? Yes 

Chrome version: 50.0.2661.102  Channel: stable
OS Version: 10.0
Flash Version: Shockwave Flash 21.0 r0

Forcing youtube to use the Flash player in Chrome gets it to play the 4K video smoothly with only 50% CPU usage.

Microsoft Edge on Windows 10 plays the 4K video smoothly with HTML5, with only 30% CPU Usage.
 

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