In samsung Galaxy s5 there is Dual Camera feature , it is a photo shooting mode that lets you capture a photo postcard using the front and back cameras at the same time.
In this feature You can use both Back and Front Camera at the same time.If you want to try this feature then follow below steps
Open your Camera App. Touch Mode Galaxy Camera – Camera Mode Button and then touch the Dual camera thumbnail.
A thumbnail view taken from the front-facing camera displays on the left side of the camera viewfinder.
To resize the thumbnail image touch and hold it and then release. You will see a white frame around the thumbnail. Touch Widget Resize handle to adjust the image size. When you are satisfied with the new size release the thumbnail image.
Touch Widget Resize handle to display the border choices available for the thumbnail image. Touch Instant pic to add a border with the current date along the bottom or choose a frame, such as Stamp.
Aim your device at the subject and touch the screen to focus on a specific area. When the focal point turns green touch the camera shutter button.
You can also touch Switch Camera to switch between the front and back cameras, which will switch the back camera image to the thumbnail view and vice versa.
How to record Video in Dual Mode
Touch Mode Galaxy Camera – Camera Mode Button and then touch the Dual camera thumbnail. A thumbnail view taken from the front-facing camera displays on the left side of the camera viewfinder.
Note: You can change the thumbnail image border only in camera mode. But you can adjust the image size after switching over to recording mode.
Aim your device at the scene and then touch Record Movie Button to begin recording.