Why setting -r 30 still gives fps=15 in ffmpeg? Why setting -r 30 still gives fps=15 in ffmpeg?

command:

fmpeg -loglevel verbose -pixel_format mjpeg -s hd720 -r 30 -i /dev/video1 -f libx264 -preset ultrafast -tune zerolatency -crf 23 -f matroska tcp://192.168.1.43:5000


output:

frame=10497 fps= 15 q=22.0 Lsize=  253990kB time=00:11:39.76 bitrate=2973.4kbit
fps= 15 represents the encoding speed, not the output file framerate.