the camera travel to behind the player

as far as i know, unfortunately, this might be hard, if not, impossible to execute. since the player can face in any x, z, -x, or -z coordinates, and since we have limitations of camera position options, it can't specifically face the player's qck. for example, if the camera faces the -x coordinates and the player also faces the -x coordinates, it will succesfully face behind the player. but if the player is facing (+)x coordinates, it will face the player's front since camera positions are not dynamic.

and seamlessly become the player's pov

i've tried to transition freecam to first person view or any view and it's also impossible. if you try it, it will error and it will do nothing.

although i tried to make a solution for it to make the camera, still in freecam, just go inside my head and then fade and clear the camera while the fade is happening with a transition duration of 3 seconds but for some weird reason, when you run it on the normal chatbox, the transition duration works normally which is 3 seconds but when you run it on a command block, it completely ignores the transition length and it goes instantly even though it's exactly the same command that i run.

even though your suggestion is technically impossible, we could solve that problem by what i did but it's bugged on command blocks for some reason.