MarsSeed [1] filed a deletion request for ffmpeg-gpl-bin [2]: This package is improper. Links to an ever-changing binary tar file. Like a VCS package but for pre-built package.
As it is, it is not useful to have as a pacman package. AUR helpers won't ever notify the user that there is an update. Also the build is not reproducible. [1] https://aur.archlinux.org/account/MarsSeed/ [2] https://aur.archlinux.org/pkgbase/ffmpeg-gpl-bin/
