commit 2827295703c74e3c119df9a435aa856e268c2ea9 added vaapi support. It get's detected automatically. I did a short test and it seems to work fine.
Created attachment 357546 [details, diff] mpv-vaapi.patch Please commit attached patch and do 'cp media-video/mpv/mpv-0.1.{3,4}.ebuild'.
Thansk, commited + 02 Sep 2013; Sergey Popov <pinkbyte@gentoo.org> mpv-9999.ebuild, + metadata.xml: + Add VAAPI support via USE-flag, wrt bug #481118 + 02 Sep 2013; Sergey Popov <pinkbyte@gentoo.org> +mpv-0.1.4.ebuild: + Version bump, wrt bug #481118