Use ffmpeg to convert RTSP stream for nginx server to deliver

Question

I have nginx server running on a Raspberry Pi4, delivering weather data. I have an IP camera that delivers an RTSP stream. ffmpeg can read this and convert to a MPEG file. I want ffmpeg to convert the RTSP stream into an output that nginx can deliver. I tried this:

ffmpeg -i rtsp://192.168.1.18:554/1/h264major -c copy -listen 1 -f ogg http://192.168.1.15:80

That being the IP and port where nginx resides. I get a

Permission Denied

error from ffmpeg. nginx points to /var/www/html/. Can I use ffmpeg to place an HTTP stream in a folder within the HTML folder, so that nginx can deliver it?