Huge delay using beta4 rtmp

[S-Przybylski]

Dear @blakeblackshear
dear contributers,
first thanks a lot for this brilliant piece of software!
I tested beta4 the last days. I enabled the rtmp stream: The stream is 15 seconds delayed compared to the debug mjpeg stream. I played with several values, configurations, at the end without success.

I read that the GOP of FFMPEG is set every 250 pictures. This GOP seems to be needed for the rtmp client first to start. Because my camera work with 20 fps, i imagine that this could be the reason for that but i am not sure if that is correct at all. If I try VLC it also takes time to see the stream too (much more than 15 sec).
https://stackoverflow.com/questions/43868982/low-latency-dash-nginx-rtmp/45370210#45370210

Currently I have disabled the rtmp stream and the HA Frigate integration automatically switched over to the mjpeg stream (after a reload of Frigate integration) wonderful feature!!

Does you / someone have an idea to reduce the delay of the rtmp stream?

Host: Dedicated RASPI4 with Coral 4GB 32bit Docker container (CPU 150-240%).
Camera: 5 x 8MPs CAMs with two streams: 3840x2160 20fps (only clips for some cams) and 720x480 20fps for detect and rtmp (if set to 5 fps on camera there is a additional delay visible)
Configuration: My configuration is copied from the beta4 readme. With detect fps = 5. I only added nobuffering to fasten the streaming a little bit:
input_args: -avoid_negative_ts make_zero -fflags nobuffer -flags low_delay -strict experimental -fflags +genpts+discardcorrupt -rtsp_transport tcp -stimeout 5000000 -use_wallclock_as_timestamps 1
The standard Log shows no errors!

Perhaps also interresting: arut/nginx-rtmp-module#378