This is based on this simple guid. It is a much easier media solution than DLNA. jailed nginx configuration:

server {
    listen       80;

    location / {
        root   /media;
        autoindex on;
    }
}

Add user www to the group that can access the media folder:

pw groupmod media -m www

Preferrably media group should only have readonly access to media/.

Now set up pf in host:

rdr proto tcp from any to any port <external_access_port> -> <jail_ip> port 80