[FFmpeg-user] Question about using ffmpeg to convert a sequence of images to video

[陈阳]

Hi guys,
       
     I use ffmpeg to convert a sequence of images to a video, i find that after i feed first image to it and almost 6 seconds later ffmpeg output first video frame to me.
I use command as follow:
ffmpeg -f image2pipe -r 100 -i pipe:0 -f flv -r 100 -tune zerolatency -preset ultrafast -bufsize 2M -codec:v libx264 -codec:a libmp3lame -bf 0 -muxdelay 0.001 -s 478x850 -b:v 2M pipe:1
     Is my options is right?
    Or others led to this result?
    How can i get first video frame quickly once i feed the first frame?
    By the way, i create a question in stack overflow, maybe you could answer my question at here(https://stackoverflow.com/q/49646564/8782964)