VidiWallpaper is a free application that lets you play a video clip live on the background of your main screen. You can choose the video and set the time to play it. The app is extremely easy to use, so you don't need to have any prior knowledge of Android to make use of this application. You just need to follow the instructions that'll be displayed on your screen.

Usage direction:

In order to be able to play the videos, you need to allow the app to access your device's storage. This is so that it can get access to the videos that are stored on your device.