Since 12 February 2014 ffmpeg supports x265 encoding. Please add a x265 use flag (and a x265 ebuild of course).
Created attachment 371892 [details, diff] Patch to add x265 support via new x265 USE flag This patch adds necessary changes to include x265 support in ffmpeg live ebuild. New USE flag x265 is proposed. Also, depends on media-libs/x265, which is not yet in portage. This, this one depends on #485352.
+ 12 Mar 2014; Alexis Ballier <aballier@gentoo.org> ffmpeg-9999.ebuild: + add x265 support, bug #502068 by Michal Feix +
media-libs/x265:0 (media-libs/x265-9999::gentoo, ebuild scheduled for merge) conflicts with <media-libs/x265-0.9:= required by (media-video/ffmpeg-2.2_rc2::gentoo, ebuild scheduled for merge) Why not x265-9999?
(In reply to darkbasic from comment #3) try it and you'll see...