I've had some issues capturing video with sound on Ubuntu. gtk-recordmydesktop got video OK but no sound. Here is what finally worked for me:
Then you don't need to change anything in gtk-recordmydesktop.
Install alsa-utils if you haven't already: sudo apt-get install alsa-utils
and make sure you really don't have pulseaudio: sudo apt-get purge pulseaudio gstreamer0.10-pulseaudio
As removing pulseaudio doesn't remove the gstreamer pulseaudio. Also make sure that gstreamer-properties is set to autodetect for sound output.
Once you do that, go into alsamixer in terminal: alsamixer
then hit the tab button on your keyboard to move over to capture.
There should be a list of capture devices and a volume control for capture. Put the volume for the capture at a suitable level, then select your capture device by pressing space on the capture device you wish to use. But this is based on my IBM T41. Your computer may be different. Mix is the device that your sound outputs on, so you'll want to capture it.
