4ch digital video recorder 8ch 16ch, video and audio IO port: RS-485 Backup: ... .264 DH.264 compression camera 16ch 8ch 4ch digital video recorder ModelHDVR3504HDVR3508HDVR3516PriceMOQ:10PCS : HDVR3504: 51$, HDVR3508 58$, HDVR3516 78$Video standard ...