The video capture procedure varies depending on platform.
The most successful captures have been performed using Yukon.
The wiki page linked describes how to compile, but running is complicated by the fact that Chromium currently requires that we compile to 32-bit, even on 64-bit systems. On 32-bit platforms yukon should work out of the box. On 64-bit platforms, you'll need to
before launching cppoh. The stock yukon script does not do this for you.
On either type of platform, yukon hijacks the GL library calls, allowing it to grab frames at the appropriate times. The default hotkey to start the capture is F8. As of this writing, yukon's configuration code is broken, so changing the hotkey or any other settings (FPS, etc) requires editing the code.
Current experience is that yukon's video capture works about 60% of the time, apparently randomly. The other 40% of the time it produces files their player won't play.
Untested, but commercial offerings such as fraps should work fine, as they do with other Ogre based applications.
Video capture on the Mac has not been tested yet.