Gravando com Mencoder

From here you have to press 's' to take the snapshot. The snapshot will be saved in your current folder as shotXXXX.png. If you want to record continuous video:
$ mencoder tv:// -tv driver=v4l2:width=640:height=480:device=/dev/video0:forceaudio:adevice=/dev/dsp -ovc lavc -oac mp3lame -lameopts cbr:br=64:mode=3 -o .avi
Press Ctrl+Z to end the recording.

in reference to: http://wiki.archlinux.org/index.php/Webcam_Setup#VLC (view on Google Sidewiki)