How to record video and audio from a Linux desktop?

Recording a video from Linux desktop content, like for creating a screencast presentation, is quite simple with recordmydesktop or its GUI version gtk-recordmydesktop.

However if you want to capture the system sound as well (not what you might speak live into a microphone), it gets a bit more difficult. Here is one possible solution with the pulseaudio sound server (available by default in Ubuntu Linux):

1. Install pavucontrol by executing sudo apt-get install pavucontrol.
2. In gtk-recordmydesktop, go to "Advanced -> Sound -> Device" and change the value from "DEFAULT" to "default".
3. Start pavucontrol.
4. Do a test recording with gtk-recordmydesktop and, while it's recording, in pavucontrol go to tab "Recording", there in entry "ALSA plug-in[recordmydesktop]:ALSA capture from" change the value from "Built-in Audio Analog Stereo" to "Monitor of Built-in Audio Analog Stereo".
5. In tab "Input devices" use the dropdown on the bottom to display also monitor devices, look for the ""Monitor of Built-in Audio Analog Stereo" device and make sure it's not silenced and the volume gauge is at 100%. When something is playing through your speakers, you have to get a signal showing up there, independently of if you're recording at the moment.
6. Record with gtk-recordmydesktop as you're used to do.

This solution was taken from ubuntuforums.org thread 1509398.

There is also another solution involving only ALSA and the snd-aloop kernel module for recording from a loopback soundcard. However I could not get it to work.