Processing Camera stream in Opencv, pushing it over RTMP (NGINX RTMP Module) using FFMPEG

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Output video: https://youtu.be/VxfoBQjoY6E

Explanation:

I want to: Process camera stream in Opencv and push it over to RTMP server. I already have NGINX (RTMP module) set up and I have tested streaming videos with both RTMP (Flash Player) and HLS.

I am reading the frames in a loop and using 'subprocess' in python to execute ffmpeg command. Here's the command I am using:

command = [ffmpeg,
    '-y',
    '-f', 'rawvideo',
    '-vcodec','rawvideo',
    '-pix_fmt', 'bgr24',
    '-s', dimension,
    '-i', '-',
    '-c:v', 'libx264',
    '-pix_fmt', 'yuv420p',
    '-preset', 'ultrafast',
    '-f', 'flv',
    'rtmp://10.10.10.80/live/mystream']


import subprocess as sp
...
proc = sp.Popen(command, stdin=sp.PIPE,shell=False)
...
proc.stdin.write(frame.tostring()) #frame is read using opencv

Problem:

I can see the stream fine but it freezes and resumes frequently. Here's the output of FFMPEG terminal log:

Stream mapping:
  Stream #0:0 -> #0:0 (rawvideo (native) -> h264 (libx264))
frame=  117 fps= 16 q=22.0 size=     344kB time=00:00:04.04 bitrate= 697.8kbits/s speed=0.543x

It mentions speed at the end. I believe it should be close to 1x. I am not sure how to achieve that.

And I am on the same network as server, I can post my python code if required. Need some ffmpeg guru to give me some advise.