How to fix linear audio delay increase ?

[Joergi]

Dear all,

how do I fix the following audio video synch issue:

I captured a DV video to hard disk, so now I have an AVI with DV codec and PCM audio.
The audio is not synchronized with the video. At the beginning of the video everything is fine, at the end the audio is about 2500ms too late. The audio delay increase seems to be linear.

Length of the video: 30.098 frames with 25fps = 20:03,920 (min:sec,ms)
The audio delay increases by 125ms in 1 minute.

Of course I read Nicky's guide on http://nickyguides.digital-digest.com/audio-synch.htm. I tried AVI Info mentioned in the guide but it won't load the video.

The error message of AVI Info is:
"Hmmmm There appears to be a problem opening this file. Please send the text of this message to lee.page@terabit.demon.co.uk."

Unfortunately the above email address is invalid, I guess the author does not the support the software anymore :-( ?
The website of AVI Info (http://www.terabit.demon.co.uk/)is invalid, too. Does anyone know if there's a new valid URL for a homepage ?

I opened the file with GSpot and it says that the file has a corrupt AVI header. As a result GSpot doesn't show me the playing time.

So now I tried Adobe Audition (fka Cool Edit) to correct the synch issue but I didn't suceed.

I used Effects->Time/Pitch->Stretch...

Now I have the choice between contant or gliding stretch. In my case the audio delay increases so I chose gliding stretch.

I don't understand the initial and final value slider. What do I have to adjust there in my case ?

And I don't understand the stretching mode. What do I have to select there in my case ?
1. I want to preserve the pitch of the video.
2. I want to preserve the total playing time of the video.
3. I want to preserve the 48.000 Hz.

The manual of Adobe Audition is not the best. Could anybody give me a hint on what to do to correct the audio synch problem ?

Best regards,
Jörg

[Atamido]

I would try using DivFix (http://divfix.maxeline.com/index.php?target=showdoc&docid=356) to see if it will fix your AVI so one of the other tools can use it. Or you could try AVI-Mux GUI (http://www-user.tu-chemnitz.de/%7Enoe/Video-Zeug/AVIMux%20GUI/index-eng.html) to see if it could open the file and allow you to change the framerate of the video.

[Joergi]

Thanks for your answer Pamel but DivFix does not support AVIs larger than 2GB. My AVI is 4,5 GB large.

I think the corrupt header is unimportant. I already tried and successfully converted the DV AVI with AviSynth and CCE to an elementary MPV MPEG2 video file and a linear PCM WAV file.
But the problem is still that the audio and video part are not in synch.
So I'd like to keep the MPV file as it is and manipulate the audio file (e.g. with Adobe Audition) before multiplexing both to a synchronous MPEG2 video file.

[SomeJoe]

Play back your DV tape on your camcorder with video/audio outs going to a TV. This will tell you if the footage was recorded OK in the first place.

If it's OK there, you have one of 2 issues:

1. Capture problem. Try a different capturing program.

2. Unlocked audio on the camera with a severe mismatch between video oscillator and audio oscillator.

Since your original DV file is exhibiting the issue, I'm thinking the problem lies either in the camera or the capture card/capture process.

For more info on unlocked audio and why it can be a problem, see Adam Wilt's Page (http://www.adamwilt.com/DV-FAQ-tech.html#LockedAudio).

[Joergi]

Dear SomeJoe, thanks for your hints, but:

The source video came from an old analog Hi8 tape and was transferred to VHS tape. I just had the VHS tape and a SVHS VCR. I borrowed a DV cam from a friend and used the cam as an analog to digital converter. I had to give the cam back to my friend the next day.

So now I have to live with the DV file that I have on my hard disk. I am not interested in the root cause of the asynchronous audio (capture or unlocked audio problem or whatever). I just want to fix the existing audio to have it in synch with the video again. That's all.

So again: How can I modify the audio stream by the use of any audio software (Sound Forge, Adobe Audition or whatever) and remove the 150ms audio delay increase per second ?

[SomeJoe]

Originally posted by Joergi
So again: How can I modify the audio stream by the use of any audio software (Sound Forge, Adobe Audition or whatever) and remove the 150ms audio delay increase per second ?

Don't know about Audition, but Sound Forge 6.0 can do time stretch/compress without altering pitch or sample rate. This would be the preferred method to make it match the video. However, even this may not be exact enough to maintain solid sync. It may take some trial and error.

[erratic]

Fixing sync problems is even easier with Vegas 4.0. Put the AVI file on the timeline, click on the audio track, hit U to ungroup (unlock) it from the video, grab the end of the audio track with the mouse, and hold down the Control key while stretching the audio track. In the preferences there's a setting to preserve pitch when stretching audio events.

If you make the audio and video track the same length the sync should be fixed, but I have noticed that AVI files captured with a DirectShow capture program (Virtual VCR in my case) often have an audio tack that is slightly longer than the video track (even if there's no sync problem). If you have to fix a gradual sync problem in such an AVI it can be a matter of trial and error, but you can check the results immediately on the timeline.