When I view it in IE on W7, I get only up to 720p option, and above that a tab that says "Missing options?" takes you to a page that says this...
"YouTube videos missing quality options on this browser
YouTube videos are available in many formats and resolutions. However, some browsers do not support newer video formats. This means these browsers may only have one or two video formats to choose from. We recommend upgrading your browser or operating system for the best viewing experience.
Below are some browser and operating system combinations that support YouTube's high-quality video formats:
•Google Chrome (all operating systems)
•Internet Explorer or Edge on Windows 8.1 or newer
•Safari on Mac OS X 10.10 or newer
•Firefox on Windows 7 or newer and on Mac OS X 10.10 or newer"
YouTube uses HTML5, though there is an extension for IE that blocks it and allows you to view with Adobe Flash.