Recordbox camera not working.

Hi I'm on version Recordbox 5.6 with a Mac book pro on 10.12.6. 

Please can you help advise why I cannot get a usb camera or even the facetime camera to display, both the preview and on button are greyed out. I have tested my USB cam in another application and its working. In prefs I have under video enabled "Monitor USB Camera" on and off its made no difference. This function is quite important for my live performance if you can help thanks.