events { ... }
http {
    include mine.type; 
    server {
        listen 80;
        server_name example.com;
        root /var/www/example.com; 

        location ~ \.mp4$ { 
            # match any file ending with .mp4
            root /var/www/downloads/;
            mp4;
            mp4_buffer_size 4M; 
            mp4_max_buffer_size 10M; 
            # Max buffer 10MB, when over the threshold, 
            # It will return: 500 internal server error.
        } 
    }
}