Unity 2018.1.7f1 android renders video background but using the latest version Unity 2018.2.3f1 for android you get a black screen. However tracking still works.
This was reported initially on 6th August by tabworld and is a problem for a number of developers. As you can see from tabworld's thread.
The problem exists for my app and all the EasyAR Unity examples
As yet there has been no response from EasyAR about a fix