Yes, the Nikon 1 J5 can be powered from the mains using separately purchased optional accessories. These are the Nikon power connector EP-5F combined with the AC adaptor EH-5B (both of which are shown below). The AC adaptor connector fits into the battery compartment of the camera which in turn is connected to mains electricity via the AC adpator.
YouTube Videos: Nikon 1 J5
Although the camera is capable of shooting video in 4K, it can only do it at a frame rate of 15 frames per second which is too low for the kind of video quality that YouTube viewers expect.