Re: Trouble synchronizing audio/video with SG

Subject: Re: Trouble synchronizing audio/video with SG

From: Muraviev Dmitry <email@hidden>

Date: Fri, 13 Jun 2008 02:07:11 +0400

Delivered-to: email@hidden

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On 09.06.2008, at 13:18, Muraviev Dmitry wrote:

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?

I have reviewed the list and found a problem similar to mine: http://lists.apple.com/archives/quicktime-api/2005/Jul/msg00091.html

But I did not find a solution to this problem.

Is it possible to synchronize audio and video data with high accuracy using Sequence Grabber API?

I have tried to do this using a comparison of audio channel timeBaseTime value with sequence grabber timeBaseTime value. (As far as I understand, audio and video channels initialized with a slight delay) And I got good results. But I don't sure that this always works and that it's the best way to synchronize audio and video data.

All I need is to get the compliance of timeValues of the video and audio channels returned by sgDataProc.

Thanks in advance!

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References:
	>Trouble synchronizing audio/video with SG (From: Muraviev Dmitry <email@hidden>)