Camera2 API was enabled on Android 5.0 to give the software applications access to the low level functionality of a camera hardware such as: Slow motion, RAW image capability etc.
To be able to use the Google Camera RAW image capture, Slow motion, manual control and other features Camera2 API works with HAL3 version.
How to flash the Camera2 API?
Flash this zip file using a custom recovery such as TWRP recovery.
The Camera2 API enabler adds following line to the build.prop file:
The build.prop file is under /system directory so the device must have ROOT access to be able to flash this zip file.