Problem capturing audio and video on Linux: audio and video out of sync

[any ANONYMOUS forum user]

I am trying to capture video (and audio) from a TV source (mainly VHS player, but also analog cable).

But the audio becomes progressively out of sync (slower) with the video. This also happens when just playing the captured video (as opposed to recording it on disk).

The stats:

Linux, F11.
P4 2.6GHz, 2G RAM
Pinnacle PC Pro capture card (Conexant chip)

I have tried FFMPeg, and Mencoder/MPlayer. Both give the same results. After about 10 min, the audio is about 3 to 5 seconds behind the video. And that offset continues to grow as the video progresses. I last tried Mencoder, with the following command:

mencoder -tv device=/dev/video0:input=1:adevice=/dev/dsp1:amode=1:immediatemode=0:audiorate=48000:mjpeg :decimation=1:norm=ntsc -vf harddup -vf expand=::::0:1 -mc 0 -o /mnt/xfs/vhs.avi -noskip -forceidx -ni -oac copy -ovc raw tv://

Any help with this will be greatly appreciated