Using composite desktop effects in conjunction with X.org 7.4 (or previous) is causing some trouble to possessors of ATI and Intel cards. This version of X.org is included in Ubuntu 8.10 as well as in Opensuse 11.1 and Fedora 10.
When a video is played, no matter with which player, black flashes appear through the video.
I must also point that this how-to was tested under Ubuntu 8.10 Intrepid Ibex with ATI Radeon HD4850 using the proprietary drivers.
There can be several different solution for the problem, what is the best one for you depends mostly on how much computational power you have under the hood.
For a powerful machine the best-looking solution is to set up your player of choice to play videos avoiding that extension. If your player of choice is the dafault Totem or any other gstreamer based player you need to access the gstreamer configuration dialog execing in a terminal:
Then go to the [ Video ] and select [ X Window System (No Xv) ] as output device.
If you happen to use VLC you just have to go to [ Tools ] -> [ Preferences ] and then to [ Video ] and select [ X11 video output ] on the output combo box.
Disabling XVideo will disable the hardware acceleration for video playback, raising cpu usage significantly. This might be undesirable with less recent hardware.
If this is your case you should disable compositing effects (3d desktop effects) and wait for a corrected version of X.org, which should be in Jaunty Jackalope.
Latest NVidia propietary drivers also appear to work around the issue, thus solving the problem.
If this helps, comments will be appreciated 🙂