The i810 driver (versions 1.7.0 and above) need a patch to get Xv working on
the i965 video cards. Otherwise starting any Xv application causes X to crash.
The patch, by one of the Intel X devs, can be found at
https://bugs.freedesktop.org/show_bug.cgi?id=8594
I simply copied the 1.7.2 ebuild and created an -r1 in my local overlay,
adding:
PATCHES="${FILESDIR}/${PV}-fix_xv.patch"
(that file being exactly what Wang Zhenyu posted in the bug discussion linked
above).
This patch fixed the Xv issue for me and at least one other person, and based
on list discussions it seems several people have had this exact problem with
the 1.7.x i810 drivers.