How do people use videofiles as a capture source for cameras? Sometimes you see people streaming videos through apps that are only supposed to use the device camera. My question is, how can you choose a video file to be your capture source for the camera? I'm thinking it may not be possible to achieve on the regular Android phones. In this case, is there a certain program or Android emulator for PC, which you can configure to capture a certain videofile as if it were a camera input?
Thanks in advance.
Say you want to record yourself playing "Candy Crush". The easiest way to do this is to download an android emulator here: http://www.bluestacks.com/
And then download the game you want to record and a screen recorder. 
(I recommend OBS studio.)