I would argue that multimedia came before win95. You can see many sound+video+more integrations on program-level before then (The installer for Command&Conquer is a legendary example. There'sa reason why the first setting the installer asks of you is your soundcard details.)
But it was with win95 the concept was embraced by an operating system geared towards it. And that's what allowed for many of the whacky UI designs of media players that came not long after.
I guess the advent of the affordable CD drive meant that win95 was where it was becoming more accessible. That and Internet connections becoming more mainstream.
Remember when games said things like: "requires a 2x cd rom drive"?
I'd say 95 was around the peak. It didn't start it, but it ensured it got to be as massive as it was.
That obsession with weirdly shaped windows with no window manager decor
