I use xvidcap. To solve the sync out I have installed the PulseAudio mixer (pavucontrol).
Also I choose a low fps, because I use a laptop which is not very powerful.
First I run pavucontrol:
$ pavucontrol
Then I run xvidcap in this way:
$ padsp xvidcap --fps 10 --cap_geometry 1440x900+0+0 --file "file1.mpeg"
padsp
is the pulseaudio wrapper. Options are only an example, you choose your own.
Then go to pavucontrol, in the recording tab. This tab works only when a video program is running. Here you can choose the audio source you want to record. Finally start recording.