i disable the Sky from the VRWorld, but did not find where to enable the camera video behind the VREnvironment. 

heres the example

http://www.nfx3d.com/Video.mp4

I need to see the camera video behind from the vr, how could i fix that?

Yes, the MixedRealityController API offers a few modes among which you can choose.

The scenario you describe should correspond to the mode:

   MixedRealityController.Mode.ROTATIONAL_VIEWER_AR 

(i.e. Stereo AR with rotational head tracking)

In the ARVR sample you can set the Mode in the TransitionManager.cs script.