Just the video processing.
They are just mirror images. Kind of like the same thing you can do with a photo... "flip" it with a photo editor.
This is an optional setting on a lot of video cameras. You may have experienced this taking a photo with your cell phone before depending on if you are using the front or back camera.
Imagine driving in your car and you turn around and face rearward and take a picture. YOUR view is that if left-right orientation. Now imagine that same scene, still behind you, but you are looking forward. Things that were on your right when you were facing them directly are now over your left shoulder.