I had the same issue. If u use Wi-Fi for Internet access, try using a different Wi-Fi network when downloading or restart your Wi-Fi router. Try using an ethernet cable for wired Internet access instead of using Wi-Fi.
Also check for updates for your computer or for any security software you may have.
(This info is in response to a slightly different question on this forum)
I don't know what the actual answer is, but I am having the same issue. The page https://developer.apple.com/library/safari/documentation/AudioVideo/Conceptual/Using_HTML5_Audio_Video/AudioandVideoTagBasics/AudioandVideoTagBasics.html
has some good info. And the page https://developer.apple.com/library/safari/documentation/AudioVideo/Conceptual/Using_HTML5_Audio_Video/Device-SpecificConsiderations/Device-SpecificConsiderations.html#//apple_ref/doc/uid/TP40009523-CH5-SW1
states
"Optimization for Small Screens
Currently, Safari optimizes video presentation for the smaller screen on iPhone or iPod touch by playing video using the full screen—video controls appear when the screen is touched, and the video is scaled to fit the screen in portrait or landscape mode. Video is not presented within the webpage. The height and width attributes affect only the space allotted on the webpage, and the controls attribute is ignored. This is true only for Safari on devices with small screens. On Mac OS X, Windows, and iPad, Safari plays video inline, embedded in the webpage." -
Which, I believe, means on the iPad, that the video plays at the resolution of the initial window (determined by the programmer), and does not naturally play on the YoutTube player, or at a higher res if you enlarge the video.
This seems to be the "problem" that we're encountering - that its a "feature" specific to Safari on the iPad. Why they do this, I dunno. In my case, the video plays at a higher res (and better) on my smaller iPhone than does on my iPad mini with Retna. Go figure.
I came upon this post, hoping to find the answer and a work around. If you get the Youtube app, and find the video through that, it will play at the highest resolution, but not through Safari. So far as I can tell.
Enjoy
Best Answer
Did you try the YouTube iOS app? You may need to change a few settings first, but I believe the YouTube app supports full quality videos - including 4K. Apple's built-in uploader from the share menu doesn't work that well.
In the YouTube iOS app, click your user image, then on the window that slides up, select Settings. Scroll down to uploads and confirm that full quality is selected for upload quality. Press the X on the top left to return to the main part of the app.
You may now press the camera button (next to the search button) on the top bar. It will ask for appropriate permissions. Try uploading from there and see if it works for you.
(I just tested this method and can confirm HD+ resolutions - also, I just noticed that this was a really necro'd post.)