It looks like there in not any easy way to screencast under Linux. The easiest way I've seen was on a screencast where the Ubuntu system shows the command 'cat /dev/video0 > test.mpg' The other options seem to be recompiling ffmpeg so that it is compiled with --enable-x11grab or installing alpha software.
From the Ubuntu Blog > Screencast with a gstreamer pipeline, I found these two applications in the comments
Istanbul is a desktop session recorder for the Free Desktop. It records your session into an Ogg Theora
video file. To start the recording, you click on its icon in the
notification area. To stop you click its icon again. It works on Gnome, KDE, XFCE and others.
Vnc2swf is a cross-platform screen recording tool for ShockWave Flash (swf) format.
And this comment stood out on the How to Create a Screencast in Ubuntu post.
Alexander Grundner - June 9, 2006
I figured out how to get xvidcap working in Dapper (gvidcap crashes for some reason).
1. Download the .deb file of xvidcap from http://www.jarre-de-the.net/computing/debian/
2. You’ll have to correct the libpng.so.2 error by doing:
$ cd /usr/lib
$ sudo ln -s /usr/lib/libpng12.so.0.1.2.8 libpng.so.2
3. Launch xvidcap:
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