In the setting Audio Source you can set it to system audio which will record the internal audio.
Now you may need to start and stop a small recording of your background outside the game. The goal is to start the app and get it in you notification tray. After you stop your first small recording it may take 20 second and you have a SCR ready in you notification tray. If it doesn't happen just try to record small video again and wait until it does.
Start the game. When you are ready to record, on android you can access the notification tray without exiting the game and start a recording while your in game. Record then when your done you can access the notification tray to stop the video or turn off the screen which will stop the video by default. (the off screen off video is an option that can be turn off in the setting)
You can delete all the wrong video afterward. In the setting you can set a folder where to save the video.
