A Brief History of Academy Award-Winning Visual Effects: A Video Essay by Nelson Carvajal
In 1977, a specific award category for visual effects was reintroduced with the current name, "Best Visual Effects." This retrospective was conceived and edited by Nelson Carvajal to music for Inception ("Time") by Hans Zimmer.
Is this use of existing content legal? As Nelson Carvajal notes, under the fair use doctrine, it is not an infringement to use the copyrighted works of another in some circumstances, such as for commentary, criticism, news reporting, or educational use.
You can read an essay about the perils of the "video essay" form ("retooling existing media in an effort to discover new meanings or alternative interpretations, while also drawing back on nostalgia and what certain images meant to different viewers") under our current system of fair use by Nelson Caravajal here.