Put 3D text in background

Hi guys

Got some footage of a guy with a guitar singing on a beach (camera facing him as he moves 180 degrees in a circle

He wants some text on the sand behind him, so as he moves the text moves too, can I do this in fcpx?

Difficult and tedious but certainly do-able. You need to investigate the masking feature and learn its limitations and interface adjustments. You will draw a mask around the talent and apply the mask to the text layer. You will hand-tweak the mask on every frame, setting a keyframe for every frame of the foreground video, because you talent's shape will change on every frame.

By the time you get a few days into this, you will find it is easier to reshoot it properly against a green screen. Then you apply the text to a clean plate of the background, shot without him in the scene. The 3D effects applied to the text are best done in Motion where the camera view will interact with extrusion and lighting.