How to download HD Youtube video on iOS?
iCab Mobile (http://www.icab-mobile.de/) is a very functional web browser with many plugins In addition to the ability to download files for local storage and then opening with other apps via iOS's native share sheets. If you can view the video in the browser, you can download it. It also offers the ability to change your browser's ID so that you can tell the server you are on a Mac or Windows desktop in order to get your desired resolution. Highly recommended tool for downloading videos at whatever resolution you want.