Dingbert on "making mediaelement.js responsive"

Hey! Thanks a ton for the tip! The volume slider still pops out when changing the width but pops back in the moment you stop moving the mouse.

If anyone searches for it in WP 3.6 look in the file
/wp-includes/js/mediaelement/mediaelement-and-player.min.js

and the part you're looking for has no spaces there (that's why i didn't find it right away :) )

b=this.controls.width()-a-(c.outerWidth(true)-c.width())

and change it to
b=this.controls.width()-a-(c.outerWidth(true)-c.width())-1

as mentioned above by Kevin.
Oh, and remember to clear the cache, like twakspot says...