Add core event on includes/functions_download.php

I would like to create an extension that plays mp4 video and mp3 audio natively in a phpBB instance when using an html5 compliant browser, without the use of bbcode, as described here:

https://www.phpbb.com/community/viewtopic.php?f=496&t=2319361

While the changes I describe work for mp3/4 on Windows browsers, they do not for iOS browsers, because the latter requires the server to respond to byte-range requests, as described here:

https://www.phpbb.com/community/viewtopic.php?f=461&t=2383226&start=15

I was able to make it work for iOS, by modifying includes/functions_download.php as described in the last link. However, there is no core event for this file that would lend itself to an extension. I am requesting an event that would permit me to incorporate the change in an extension.