Why is ffmpeg very slow artifact?

Question

Nginx

I send a stream to nginx rtmp server, it presses the stream and sends it further. Comp 2x Xeon 2670v3 24 cores 48 threads 3.1Ghz RAM 16GB SSD disk
in the veryslow preset output artifacts the server is loaded by 30-45%
tried to process two threads in slow mode simultaneously and on both threads the picture is excellent, there are no artifacts, but veryslow does not want to in which. Sending a picture 1920x1080 40Mbps

worker_priority -19;
user www-data;
worker_processes  auto;
events {
  worker_connections 8192;
  use epoll;
  multi_accept on;
}
rtmp_auto_push on;
rtmp {
  server {
    listen 1935;
    max_message 10M;
    chunk_size 8192;
    max_streams 32;
    sync 10ms;
    application potok<>{
      live on;
      record off;
      exec nice --20 ffmpeg -re -i rtmp://127.0.0.1/potok -vcodec libx264 -g 60 -preset slow  -b:v 7800k -maxrate 7800k -bufsize 7800k -s 1664x936 -x264opts nal-hrd=cbr:force-cfr=1:keyint=120:scenecut=0 -sws_flags lanczos  -acodec copy -r 60 -f flv rtmp://127.0.0.1:1935/transcode_potok;
    }
    application transcode_potok {
      live on;
      meta copy;
      push rtmp://сайт с ключем;
    }

And please don't ask why this is all =) I know about NVENC, I need it that way! =) Bittrade also cannot be raised there is a limit.

Answer 1

Try to encode on 1x Xeon, at least there is a shared cache between the cores, but it's not clear how it works on 2 processors.