Question: Does it support 1080PI 50 input?

Answer: Yes, it supports.

COFDM-904T supports 1080p 50
1080P 50 camera video input
COFDM-904T 1080P 50 receiver
1080P 50Hz monitor receiving (Please check the below video link or below youtube link)

Question: Does COFDM-904T have an audio transmission function?

Answer: If the audio from HDMI, then it supports, it does not support CVBS audio input, only have CVBS video input (Yellow). Please check the below video.