You should turn off screen blanking and screen savers while recording a movie.
Also, make sure that the picture of the mesh is wholly on screen, and is not
obscured by any other windows. This is because movies (and snapshots, for that matter)
are recorded by copying the pixels directly from the screen, rather than plotting
into an off-screen buffer. Whatever is on the screen (except for the mouse, which is
ignored) is what goes into the movie or snapshot.

On Windows, to turn off screen blanking, open Control Panel/Power Options.
To turn off the screen saver, right-click the desktop background. This
will bring up a menu, and on Windows Vista, the item to select is "Personalize".
On other versions of Windows it may be called "Properties".

On Mac OS, open System Preferences, and use the "Energy Saver" panel to turn
off screen blanking, and the "Desktop & Screen Saver" panel to turn off the
screen saver.