Not stable fps in delivery rtmp stream

[Pavlo]

Summary of the bug:

When flipping a thread with a given fps using the -vf "fps = 30" filter at the output when delivered, the value of fps fluctuates from 20 to 50-60 peaks.
The delivery of frames is controlled by ffprobe, which displays video frames and the code on JS counts the number of frames that came in a second.

This behavior is observed only with non-stable input stream, provided uniform and stable flow of this problem at the output ffmpeg is not observed.
Also, if we analyze Freeman by comparing the pkt_pts_time of received frames, the value of fps remains stable and equal to 30, as specified in the command.

For video analysis, use the module "video-quality-tools"

How to reproduce:

• Emulate the incoming stream with delays in delivery
• Accept ffmpeg input at this prompt
• Output stream also will not have stable fps

% ffmpeg -i rtmp://localhost/myapp/myStream -s 1280x720 -aspect 16:9 \
-c:a aac -b:a 64k -ac 2 -ar 44100 -c:v libx264 -b:v 1500k -minrate 1500k \
-maxrate 1500k -bufsize 700k -profile:v main -level 4.0 -vf "fps=30,format=yuv420p" \
-x264opts "keyint=60:min-keyint=60:no-scenecut" -preset veryfast \
-tune zerolatency -threads 0 -f flv rtmp://localhost/myapp/myStream1


ffmpeg version 3.4.2 Copyright (c) 2000-2018 the FFmpeg developers
  built with gcc 5.4.0 (Ubuntu 5.4.0-6ubuntu1~16.04.9) 20160609

Patches should be submitted to the ffmpeg-devel mailing list and not this bug tracker.