Keying/layering/chroma idk a person without a greenscreen

Now. i have this really good idea for a short film i want to do, it’s for a paper i’m starting this year.
in this film i have an actor in the middle of the shot
(this is a continuous 6 minute film, no cuts)
all it is, is 6 minutes of having the camera, on a steadycam, in front of the actor watching him walking.
sounds boring, but anyway, what happens around him is what’s important, i am planning on having many special effects done in blender with camera tracking. there will be inception like explosions, water manipulation, etc. but to do some of these things and make it look believable it will need to move back behind the actor.
and there is no way i can use a green screen for this kind of thing
is there any way. any way at all, without having to mask every bloody frame of him, to be able to key him in front as a new layer, like camera mapping, or like photoshop layering (sounds amateur but meh), so the objects that move behind him are believable

I dont think its possible to seaparate background in your case without roto or chroma key. Could you film actor on a treadmill?

Welcome to roto-land. You might want to look into After Effects for this one. The rotobrush tool would make this job an easier task.

no, treadmill is not possible for this. it’s meant to be a film where everything is normal, and then suddenly you see his imagination open up around him in the background.

mm i’m taking a paper on after effects this year, was kind of expecting to have to use rotoscope. time to learn haha

Do you need to see his feet? If not, you can shoot the areas he is walking without him. Just walk backwards with the camera. Then, shoot your actor over green screen, either on a treadmill, or just have someone walk behind him with the green screen. If you need the actors feet, it could be tough.