Microsoft today released update for Movie Creator Beta app in Windows Phone Store. This is just a bug fix update with no new features. In the last update, Microsoft added support for 4K video input with max 1080p output (on supported device models).
Previous update change log:
Support for 4K video input with max 1080p output (on supported device models)
Select photos and videos from OneDrive
Change video speed
Change caption & title font family / size / position
Miscellaneous bug fixes
Download it here from Windows Phone Store.