Assign physical camera button to another app Is there a way to assign the physical camera button to a camera-app other than the default camera app?

So, if the camera button is pressed, a specific app should start up.

If possible, it should also work in lock screen, and without rooting the device.
Yes there is a way, but your device has to be rooted.

First you have to install Xposed Framework, than download and install an Xposed module called Xposed Additions or Physical Button Music Control.

After this you can able to rebind your physical buttons.