Under the current release of Gentoo Linux, xorg-server 1.4 with xf86-video-i810 2.1.0 and above cannot replay videos (mpg, avi, wmv).  This is a bug filed under (bugs.gentoo.org : 197850).  Under Gentoo, older versions of X with the xf86-video-i810 <= 2.0.0 were able to properly display videos.

The explicit problem appears to be a triple reflection (ghost/echo) in the video displaced somewhere across the screen).  I strongly suspect attempts to enhance video display rates in the i810 driver may be at fault.  This is only evident in video program players (e.g. mplayer or totem).  It does not effect normal screen presentation with or without DRI (i.e. glxgears works fine in both contexts).

However, if anyone reading this would like to comment on the plans for DRI working across multiple X instantions (VTs) I would like to be informed about it.  It took me nearly a year to discover that current X implementations were only intended to support a single DRI terminal.  (And I always puzzled over those X log files where it indicated that DRI was not supported.)  [It is not unusual for me to run my PC with 4+ VT's with hundreds or perhaps even thousands of windows and/or sub-windows (tabs) open in a browser running for a month or more.]