Some libav video filters need opencv, please port it to multilib.
a) please be more specific why this is really needed b) patches welcome
Dep of libav/ffmpeg.
commit d93b7bbbe54791dcca57ace7779d2eb4c101467f Author: Michał Górny <mgorny@gentoo.org> AuthorDate: Wed Aug 9 22:55:36 2017 Commit: Michał Górny <mgorny@gentoo.org> CommitDate: Fri Aug 11 15:20:42 2017 media-libs/opencv: Enable multilib builds for 3.1.0 & 3.2.0