[FFmpeg-user] how ffmpeg use network streaming as input?

[zhangkai.gis]

Hi,
     I am a newbie to ffmpeg.I want ffmpeg to convert H.264 stream to rtmp.I googled it.But I always find regular file as ffmpeg's input.but my input is a stream,the stream is H.264's I frame,P frame.How can I use the stream as ffmpeg's input?
     PS: I have many device cameras.these cameras send its video and audio to my server through RTP. I parse the packages and recollect it to H.264's Frame.Then I want to send the network stream to media server(nginx+rtmp).So I have the problem above.Any good ideas?

Thanks in advance
zhangkai
2018-7-13