$ eix -e ffmpeg [I] media-video/ffmpeg Available versions: 3.2.6(0/55.57.57)^d ~3.2.7(0/55.57.57)^d 3.3.4(0/55.57.57)^d 3.3.6(0/55.57.57)^d ~3.3.8(0/55.57.57)^d ~3.4.4(0/55.57.57)^d ~4.0.2(0/56.58.58)^d **9999(0/56.58.58)^d $ grep ffmpeg /usr/portage/profiles/package.mask >=media-video/ffmpeg-4.0 ffmpeg-4.0.2 doesn't show as masked. It only shows as being keyworded ~ Perhaps related to https://bugs.gentoo.org/658658 ?
The fix from bug 658658 seems to solve this.
seems fixed long ago though