The Xbox Video team have released an update to the Windows 8.1/Windows 10 video app. The update improves your devices battery life when you play back videos from Windows file explorer. There is also a fix for a bug which showed the incorrect file size on when selecting between HD or SD downloads.
Via Xbox User Voice
Version 2.6.439.0 on Windows 8.1 includes the following:
Improved battery life when playing video files from explorer
A fix which prevented the correct download size from being displayed when choosing between HD or SD download