Android app to record audio/video without showing on screen

Question

I'm looking for an Android app that can:

• Record video and audio.
• When it's running it doesn't show the actual app on the screen. It is OK if it shows an icon in the notification bar, however.
• Compatible with Android 6.0 Marshmallow.
• If on Google Play, has decent reviews.
• Can run in background (e.g. if some other app is running, it doesn't stop running/recording).
• It is OK if the app requires either root or Xposed.

Desired features:

• Ideally, free as in beer, or cheap(ish), under $10.
• Autofocus.
• Is smart enough to stop recording if memory capacity is low and no space left to save more video.
• Can have configurable quality of video being recorded, to trade quality for lower space used.
• An extra cool feature would be to record video in chunks and be able to transfer past chunks over network (FTP/etc.) automatically to free up more space.

Answer 1

SC-OS2 or Spy Camera OS 2 is a free (with donation version) camera/video app that will allow you to take pictures and record while your phones screen is off, blacked out, in the background or on any app. It has a small and see through GUI so it can be used inside apps. Buttons on the GUI and physical buttons on your phone are used to start video and capture pictures. The buttons can be assigned actions in the donation version. Some of the options are autofocus, burst shot, zoom features, size limit on videos and can send files to an email address.