Make sure the autoplay is toggled on and play the project on your mobile phone.
Once you open the project and play it, the video should play.
You need to import the MP4 to your assets and then:
Let me know if you have any more questions.
At the moment only MP4 video format is supported and to my knowledge alpha channel (transparency video) is not supported in MP4 video format.
For the PNG images with transparency:
This node is used to move an object from one position to another.
Use this node connected to the 'On Update' event.
The node in the nodes list:
Download it from here:
In order to install this node - follow this guide: