Long ago Vine for iOS allowed users to import ready videos on their iPhones and edit to fit within seven seconds using their own app. Now the novelty is also available for those who have Android.
By updating the app and opening the camera you will already see the new highlighted option, as shown in the next image.
In addition to being able to use ready videos, the update brings a more advanced editor, where you can delete snippets or intermediate a ready video with something recorded on time and more.
If your application did not update automatically, you can download the new version directly on Google Play.