Google automatically syncs your Play Movies & TV content with your YouTube account. This enables you to watch all of your Play Movies & TV content on YouTube without having to repurchase your content. If you choose to watch said content on YouTube, however, you may be capped at 480p playback. You won’t get options to play movies in HD even if your original purchase was in HD quality.
The temporary cap seems to have been in place since early last week and YouTube says that the lack of HD playback is a result of a “technical issue.” However, YouTube did not mention when HD playback will be restored. It’s worth noting that this issue affects both rented and purchased content.
The cap only happens when viewing directly on the YouTube website and does not affect users using the app via Android, iOS, Android TV, or Chromecast. So if you’re really itching for HD playback, you’ll have options.
via Android Police