
I don’t know anything about the JVC camcorders but when using a helmet cam with my Sony TRV460 I need to switch it to P-Edit which is in the playback menu this gives you access to a sub menu for recording the image being shown on the LCD screen of the camcorder. It’s mostly a case of closely reading your manual and finding how you record onto your camcorder from a Video or TV and that’s going to be how you will record the helmet cam input.
Hope this is of help, sadly the Sony TRV460 is neither very cheap or small (it used HI8 tapes) TBH camcorders with AV in not “Digital In” are not normally at the cheap end of the market.