yes, i removed some of the original question since it was shown to not be relevant to the issue. i appreciate that maybe it would be best to write 'EDIT:' when i edit there, but then the question might become huge.. so in the interest of balance, i just cut some parts out.

"Right now, it looks to me as if your config says that a request for
/file.mp4 will be handled in "location / {}", which will just serve the
file /usr/local/nginx/html/file.mp4."

why do you think that?

there is a PHP application being served via this config that handles the routing and serving of files, including mp4s. the video files are accessible at urls that are handled via a page handler programatically. the PHP file that serves the media files outputs the appropriate headers and feeds the file to the browser as a stream.

"Also, you seem to be testing with "curl -I -r", and being surprised at
a HTTP 200 response. nginx returns HTTP 200 to HEAD requests for files."

i have been testing with this format, as recommended here by a contributor to video.js on github (https://github.com/videojs/video.js/issues/2385):

curl -sL -w "%{http_code} %{size_download} %{url_effective}\\n" 'https://www.ureka.org/file/download/17365/censored%20on%20google.mp4' -H 'Accept-Encoding: identity;q=1, *;q=0' -H 'Accept-Language: en-US,en;q=0.8' -H 'User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_10_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/43.0.2357.134 Safari/537.36' -H 'Range: bytes=0-' -H 'Accept: */*' -H 'Referer: https://www.ureka.org/file/view/17365/me-being-covertly-censored-on-google' -H 'Cookie: Elgg=htbujjg4khfj7qr1s9nbban653; _pk_id.1.e8a2=30087d194778be65.1437418823.1.1437418823.1437418823.; _pk_ses.1.e8a2=*' -H 'Connection: keep-alive' -H 'Cache-Control: max-age=0' --compressed -o /dev/null

i ran the curl command that you provided here and saw a continual stream of unreadable characters in the terminal. i am not experienced with curl in the terminal to the extent i can discern which would be the appropriate flags to use here.

i have removed the video that i posted as a test now. however, this one will remain available:
https://www.ureka.org/file/play/7369/nasa%20mars%20anomalies%202010.mp4

thanks for assisting!