Stretched audio sync. Anyway to fix?

[jaggerdss]

I have some mpegs that the audio is off sync and is progressively more towards the end of the mpeg. I have finally corrected this problem in capturing which I think was from dropping video frames ever so often but maintaining audio during capture. My question is I have a few files now that I cannot re-capture (Not playing again on sat) and I would like to try and sync the audio back on these. The problem is that a simple audio shift won't do as the audio is progressively off. Is there any program that you maybe mark the start and end of the video then match the audio start and end to correlate? (After de-multiplexing)Someone told me about HTS but I can't seem to figure that out. Any guides, programs, suggestions?

[mikiem]

THe length of audio & video tracks should match. It's sort of common for a different audio length to cause the prob you've described. Goldwave & some other audio editors will let you time stretch or compress the file to match the video.

[mazinz]

However that is not always the case. You can have a matching audio and video and still have the sync off. In such times, an app like soundforge would come in very handy. It would require you to literally speed certain sections up and slow some sections down throughout the films audio, or adding/subtracting unnoticeable milliseconds here and there. In other words a very timely project, but if the video means that much to you, go for it.

[jaggerdss]

However that is not always the case. You can have a matching audio and video and still have the sync off. In such times, an app like soundforge would come in very handy. It would require you to literally speed certain sections up and slow some sections down throughout the films audio, or adding/subtracting unnoticeable milliseconds here and there. In other words a very timely project, but if the video means that much to you, go for it.

Thanks! Is there anyway (Or program) to insert duplicate frames of video to make up for the sync problem? Funny I don't see any problems with the video but after a lengthy investigation i'm sure the audio sync problem was caused by dropping frames of video ever so often.(Not enough to notice videowize) inserting a dup frame every once in a while should have the same effect (Or better) than shrinking my audio?

[mikiem]

FWIW...

Demuxing, then comparring length of audio vs video will tell if that's the prob., and probably the easiest thing to check. If the audio length is off by *x* amount at the end of the video, and the start points are identical, then the amount it's off sync will increase from start as it approaches the x, the max difference at the end of the file.

Vegas would probably be the easiest to use for corrections because you literally just ctrl-drag the end of audio clip to match, but at the end of the day you're still just time stretching or compressing.

It is possible for the audio to go out of sync & still be the same length -- audio & video use separate clocks -- but most capture devices guard against this (one of the main design considerations).

As far as altering the video to match, usually don't want to do this unless odd or wrong fps reported -- search forums a bit & online and you'll find plenty of reasons why. RE: dropped frames, often this means dummy or dup frames were added already to maintain sync. At any rate, finding dropped frames is going to be extremely time consuming, if possible.