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Old 4 Dec 2002, 02:40 AM   #1
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Default Audio Asynch after Joining -Quick fix please!

OK, so this is the situation. Im lookign for a quick fix.

(using GordianKnot/ Virutal Dub / Nandub etc)

I recorded a a prog to my HD from a broadcast via my PCI Digital TV Card.

Durign the course of the recording the audio becomes out of synch with the video - this is fairly normal - signal imperfections etc.

Also this synching problem can be exacerbated by stopping and starting the recording due to not wanting to record the adverts/intervals.

so i do all the encoding and then estimate the audio delay values that are needed to compensate for each time the audio becomes out of synch. In fact during this recording there were approx 8 times in which the audio becomes out of synch. So i use the interleaving procedure to get it just about right with each section.

So i end up with 8 sections of avi of differeing lengths. The audio is now in synch with Audio interleaving values of between -1300ms and -15550. The synchronisation is not perfect , but it will do. This procedure is also quite laborious.

The problem come when I decide to Join each of the clips together.

the audio then becomes out of synch again.

For example: Clip 1 (audio delay value -1400) joined with Clip 2 (audio delay value -15500) results in the audio of the clip being delayed by about 400ms. Im not sure if this value of 400ms is throughout the entire length of the whole clip, but im pretty sure it is.

So, I sort of undertand why this but not entirely sure how to correct - although i did do the following but was left with a similar Asynch problem: -

basically opening the first clip in VB (or Nandub - does it make a difference) - and changing the end offset value to 20 frames.> saving this new clip and then appending the 2nd clip with the newly created clip (withthe end offset value of 20 frames).

But this does not solve the problem and the audio is out of synch by a similar value (from start to finish) as it was when appending the 2nd clip to the 1st Clip without a 20 frame End offset valyue.

Anybody can give me a few tips on the direction i should be going in.

Am i doing the right thing by fiddlign around with the End Offset value of the clip that will be joined with another clip?

I tend to do this in Nandub as I get error messages in Virutal Dub. i.e. - when i open the first clip in VD i wil get the message that due to the VBR audio VD will correct it - perhasp resulting in xxxxx of skew etc etc.

I can prevent this message coming up if i just press OK and then alter the end offset value (by 20 frames for example) save it, and then open the new clip.

But when I then open another clip to append to the first one (with the offset value) Vritual Dub will not allow this, stating that the audio has 2 different sampling rates.

Nandub WILL allow me to append.

what am i doing wrong?

(NB the video of each clip has the same properties, i.e bitrates etc)

Im sure I had this problem in the past, and im sure i was able to solve it by changing the end offset delay to 15 frames. Im sure Virtual Dub allowed me to append after this value was changed.

Is it not allowing me this time due to the fact that there is indeed quite a difference in the audio delay values between the audio in clip 1 (-1300) and clip 2 (-15000)?

Therefore would it be case of changing the End offset delay value of Clip 1 by much more than 15 frames?

Many thanks for any help!!
james222 is offline  


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