When capturing video from a camcorder (using either S-Video or Composite) the video captures perfectly but the TV sound is recorded on the video captured from the camcorder. Switching from Television to S-Video does not kill sound from the Television source. Television setting captures video & sound from selected TV channel correctly.
to my knowledge this should be handled by the v4l driver for your tuner chipset, through GPIO codes.
you can manually change the audio record source from the sound mixer, though