Since Flash is in its death throes, it is no longer used by Mirage 9.1 if you use a modern web browser.
However, for legacy support, Flash is still used in these scenarios, but only if Flash is installed. If Flash is not installed, the video will not play.
A YouTube video in Internet Explorer 8.
An MP4 video in Firefox on Windows XP.
An MP4 video in Firefox version 20 or earlier.
An MP4 video if the web browser does not support the "video" tag.
An FLV video if "Video support" is not selected.
Edited by: ctwist on 07-Nov-2017 15:25
Clarification: In previous releases, Flash was just used to play videos for some combinations of operating system and web browser. Mirage never used Flash for its overall behaviour.