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Trouble synchronizing audio/video with SG

Hi, list

I'm capturing video/audio using SGDataProc. To determine time difference between audio and video channels i use this code:

err = SGGetTimeBase(seqGrab, &sgTimeBase);
...
err = SGGetChannelTimeBase(audioChannel, &soundTimeBase);
...
TimeRecord vid, aud;

GetTimeBaseTime (sgTimeBase, 10000, &vid);
GetTimeBaseTime (soundTimeBase, 10000, &aud);

timeShift = (double)WideToSInt64(aud.value)/(double)aud.scale -  (double)WideToSInt64(vid.value)/(double)vid.scale;

In most cases it gives me correct result and I synchronize my movie using SGDataProc TimeValue. But sometimes it seems that I get wrong value. And audio track shifts on 3-5 frames.

Can anyone give me suggestions how can I obtain the real delta between TimeValues coming with SGDataProc with video and audio samples?

Thanks in advance!

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