Gradual out of Sync Problem

[98lwatso]

I have searched the forum but not found a clear answer.

I have this 3 and half hour MPEG2 file converted from DV AVI using MainConcepts MPEG Encoder, however the audio gradually loses sync through the file.

I was hoping I would have no problems with a file this length, but does anyone know of any fixes that will help solve the issue? There were no bad frames reported so I dont think that could be the problem.

I was wondering if it could also just be playback, and the PC is havin trouble keeping up? It was eventually going onto DVD so it would be ok if it were just the PC wouldnt it?

[tjborwn101]

In a thread located in the Capture Forum someone provided me an excellent link to the following... outstanding reading..

TJ

http://www.adamwilt.com/DV-FAQ-tech.html#LockedAudio

[Suntan]

I posted this over in another forum a few days ago...

An easier way to do it is to open your video stream in something like vdubmod or tempgenc thenopen your WAV file in audacity (or soundforge, but audacity is freeware).

If the sound is offset by a constant amount throughout the movie: advance frame by frame through the video until you get to a "notable" frame for syncing (example: first frame of something blowing up.) Then write down the time at which this happens relative to the start of the video stream. Next play the audio stream until you hear the sound that corrisponds (example the start of the explosion.) Now add silence or remove audio at the beginning of the audio stream so that the explosion happens at the same time marker (relative to the beginning of the audio stream) as you wrote down from the video stream.

If the problem is that the audio starts in sync and slowly goes out of sync as the movie progresses do the same thing except find a notable frame towards the end of the movie and then use audacity to change the Tempo of the audio stream such that the audio and video streams match at that point towards the end of the movie. That way the whole thing should be in sync.

It still takes a lot of work, but you only have to make one audio stream and the results should be more exact.


-Suntan

[MpegEncoder]

It's much easier to use VirtualDub and select the "Frame Rate" menu, under "Source rate adjustment" select "Change so video and audio durations match".

Then either frame serve (best) or create new AVI (lots of disk space) to fix the sync problem.

[Suntan]

@MpegEncoder

Yes, and correct me if I am wrong, but doesn't that change the video frame rate such that it will no longer be what it was (29.97, 23.976, 25, etc.)

This may not be a big issue, though.

-Suntan

[MpegEncoder]

@MpegEncoder

Yes, and correct me if I am wrong, but doesn't that change the video frame rate such that it will no longer be what it was (29.97, 23.976, 25, etc.)

This may not be a big issue, though.

-Suntan

The change that I usuallly see, even for long videos (over two hours), is 29.971 instead of 29.970. It's never caused any problems for me.