4ch digital video recorder 8ch 16ch, video and audio IO port: RS ... DH.264 compression camera 16ch 8ch 4ch digital video recorder ModelHDVR3504HDVR3508HDVR3516PriceMOQ:10PCS : HDVR3504: 51$, HDVR3508 ... 58$, HDVR3516 78$Video standard NTSC/PAL (Optional)Image compression H. ... input/1outputAlarm Mode Motion Detection, Sensor triggered, Video Loss, HDD Full, HDD ErrorAlarm in/out4CH ...