Another option, not to have to change once and again between Analog Stereo Duplex and Analog Stereo Output neither limit the sound source for xvidcap, is to leave Analog Stereo Duplex and use also pavucontrol when we want to change the source of the sound for gnome-sound-recorder. Like the stated for padsp xvidcap, to change where we want to record the sound from, we put gnome-sound-recorder recording, open pavucontrol and in the Recording tab we put the desired option. In this case there is no need to use padsp (xvidcap needs it because it was designed for OSS. What padsp does is to connect OSS with PulseAudio, as shown in http://linux.die.net/man/1/padsp ).

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Solution for 64 bits:

In order to install it in a x86_64 system I just have to use the –force-architecture option to the dpkg -i command.

user@host:~/Desktop$ sudo dpkg –force-architecture -i xvidcap_1.1.7jaunty_i386.deb

But when trying to run it I see that there are some i386 libraries missing. In order to easily install them I use the getlibs script.

user@host:~/Desktop$ padsp xvidcap
xvidcap: error while loading shared libraries: libtheora.so.0: cannot open shared object file: No such file or directory

user@host:~/Desktop$ getlibs /usr/bin/xvidcap
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About getlibs: http://ubuntuforums.org/showthread.php?t=474790

Step 4. Install pavucontrol in Synaptic (Needed in Ubuntu 10.04 but not in Linux Mint 10: already present)
Step 5. Open the program with padsp xvidcap
Step 6. Click on the recording button (red circle)
Step 7. Run pavucontrol, go to the Recording tab and there choose Monitor of Analog Stereo Internal Audio

Done!!

To record with sound, the program has always to be run with padsp xvidcap (for example from ALT+F2). To run it always like that from the menu: run alacarte, go to Sound and video, then to XVidCap Screen Capture, Properties and where it says Command put padsp xvidcap.

The stated is to record the system sound, that is, the one coming out of the speakers, that can be of a song or movie of our hard drive or pendrive played by Totem, of a Flash music video of a website played by Firefox, …

Nevertheless, sometimes it can be necessary to record the microphone sound, for example if we want to make a videotutorial to explain how a program works. In this case we put xvidcap in recording state, run pavucontrol and in the Recording tab we put Analog Stereo Internal Audio (without “Monitor of” ahead).

If we only want to record sound (without video) we can run from ALT+F2 gnome-sound-recorder. The first time probably it will be configured to record from the microphone. To record the system sound we run with ALT+F2 gnome-volume-control, go to the Hardware tab and in Profile we put Analog Stereo Output (it’s also possible to do this running pavucontrol and using the Configuration tab).

But when we finish we have to put again Analog Stereo Duplex in the Profile of Hardware of gnome-volume-control (or of Configuration of pavucontrol), so we can still choose the origin of the sound when recording with xvidcap.

NB: sometimes, to change from Analog Stereo Duplex to Analog Stereo Output it may be necessary to change first to Off, close, open again and then change finally to Analog Stereo Output. The same for the opposite change. If not, the computer may “not notice” that we have applied the change.

Taken from http://ubuntuforums.org/showthread.php?t=1714139

Something different in step 1 for me:
Following your link to SourceForge, I had to click on “view all files” and then select “xvidcap_1.1.7intrepid_i386.deb”

The rest of the process as already described.