Why is it taking so long to upload the nginx file?

Question

Nginx

Hello. There is a server with a channel of 1Gbps. There are video files. When playing a regular video, the video starts for a very long time. Downloading metadata to start playback takes 4 seconds (4MB in 4 seconds) . At the same time, there are no speed limits on the server. If you put it on download, it gives out full 10Mbps (This is my Internet speed), and this speed is both directly in Google Chrome and through IDM, for example.
I began to think what was the matter, read more about the HDD and tried to add aio on; added
directio 512 caching;
output_buffers 1 512;
At the same time, on other sites, the data necessary to start playing the video takes an average of 1-1.5 seconds (downloads about 4MB in 1-1.5 seconds), what could be the matter? How to speed it up. At the same time, I checked it without third-party users, that is, the load on the server is generally minimal.
on the server 16GB of RAM, Inter Core i7 and 1 Toshiba DT 1TB DT01ACA100 SATA3 disk
Or is this the ceiling for speed with a Sata disk?
PS Here is the config for Location ... mp4 {} Only this is added to the default config and nothing else. The rest of the config is default from Nginx 1.16.0

mp4;
                mp4_buffer_size 5M;
                mp4_max_buffer_size 10M;
                access_log off;
                expires max;
                limit_conn addr 2; // Ограничивается количество запросов с 1 IP
                aio on;
                directio 512;
                output_buffers 1 4096k;
                sendfile on;
                sendfile_max_chunk 4096k;
                tcp_nopush on;
                tcp_nodelay on;
                gzip off;
                gzip_static off;