Please check whether the use of 'einstall' in this ebuild is actually needed. From a quick glance at the Makefile, it seems to have proper support for DESTDIR. Therefore, if possible please replace the call to 'einstall' with proper 'default' or 'emake DESTDIR="${D}" install'. Thanks.
commit 770a27165421134a6f62be44308f19291ee36bfd Author: Sergey Popov <pinkbyte@gentoo.org> Date: Thu Aug 3 16:39:58 2017 +0300 media-video/recmpeg: bump EAPI to 6 Drop unneeded use of einstall Gentoo-Bug: 521750 Package-Manager: Portage-2.3.6, Repoman-2.3.1