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sven_x · 29th October 2013, 08:44

I have solved such a problem by time-stretching audio (not cutting) with an advanced audio editor, such as Steinberg Wavelab. It is a tricky procedure.
First you have to write down the dealy times that your video has at several points.
You will get a list of this kind:

Code:

0       0 ms
5min   200 ms
15 min 200 ms
20 min 100 ms

As you can see, the delay is not equally distributed.
To be able to correct the delay you have to calculate the Delta values of the delays.

Code:

0       0 ms     0
5min   200 ms  0,2
15 min 200 ms    0
20 min 100 ms -0,1

In this example you have to stretch the audio parts
(0...5min) to (running time + 200 ms)
(5min...15min) do nothing
(15min...20min) to (running time - 100 ms)

Of course one should a use a algorithm that does not change pitch.

How do you get the delay times?
Well, that is the tricky part. You can do it by trial. Most video players have an option to delay audio for a fixed number of milliseconds. Just play with that value, until audio is synchronized to video. The accuracy of this method is about 100ms at each point. Then go, say one minute forward in the video and check synchronisation again. If the video is not in sync anymore, you have to search again for a proper delay value at this point.
Needless to say - the whole procedure is very time consuming.

29th October 2013, 08:44	#4 \| Link
sven_x Registered User Join Date: Oct 2011 Location: Germany Posts: 39	I have solved such a problem by time-stretching audio (not cutting) with an advanced audio editor, such as Steinberg Wavelab. It is a tricky procedure. First you have to write down the dealy times that your video has at several points. You will get a list of this kind: Code: 0 0 ms 5min 200 ms 15 min 200 ms 20 min 100 ms As you can see, the delay is not equally distributed. To be able to correct the delay you have to calculate the Delta values of the delays. Code: 0 0 ms 0 5min 200 ms 0,2 15 min 200 ms 0 20 min 100 ms -0,1 In this example you have to stretch the audio parts (0...5min) to (running time + 200 ms) (5min...15min) do nothing (15min...20min) to (running time - 100 ms) Of course one should a use a algorithm that does not change pitch. How do you get the delay times? Well, that is the tricky part. You can do it by trial. Most video players have an option to delay audio for a fixed number of milliseconds. Just play with that value, until audio is synchronized to video. The accuracy of this method is about 100ms at each point. Then go, say one minute forward in the video and check synchronisation again. If the video is not in sync anymore, you have to search again for a proper delay value at this point. Needless to say - the whole procedure is very time consuming. Last edited by sven_x; 29th October 2013 at 09:30.