# test ffmpeg cp sdp to answer.sdp 

ffmpeg -re -f v4l2 -i /dev/video0 -pix_fmt yuv420p -s 320x240 -vcodec h264 -preset veryfast -g 1 -f rtp rtp://127.0.0.1:5789

# ffplay

ffplay -protocol_whitelist "file,udp,rtp" -i answer.sdp