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  1. Hi guys and gals,

    I'm very new in this video and audio subject and I have problem with syncing.

    Basically, I have 2 medias (A and B) they contain the same thing. However, media A has better video, and media B has better audio. So, I want to have a new media that contains video A and audio B.

    Video A: 30fps with Variable Frame Rate.
    Video B: 23.976fps with Constant Frame Rate.
    I have been trying to use audioscale so video A and audio B have the same length, but the audio at the beginning is too slow, and near the end is too fast. I believe it's because video A is VFR.

    What should I do?
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  2. Line up the audio tracks in Audacity and see whether they actually drift, where, and why. VFR video shouldn't have anything to do with it.
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  3. I'm sorry, I'm really new in this thing so I know nothing. I don't know how to line-up the two audio. I tried to open two audios, it shows different windows. Do you mean that I should do alt-tab to compare?

    I did try to do my home work. I read that some people believe that Audio doesn't have fps...but some people believe that Audio does have. This makes me more confused.

    Btw, I did try to search and I found that there is a Presentation time stamps (PTS). Maybe this is the answer? Can I extract the PTS so my audio can be synced with the video?
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  4. Regarding Audacity, install the ffmpeg plugin. Then simply drag and drop the two videos into the same window and you should be good to go to line up the tracks.

    What format are your two videos in?
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  5. Ahh...yes, drag and drop works. Thanks for trying to help me.

    Audio A length is 22m 44.59sec
    Audio B length is 22m 48.064sec

    After I change the tempo of Audio B to match Audio A, Audio B became 22m 44.58sec. There is 0.01sec difference. The drifts are probably around 0.7 sec max, sometimes less. But it is enough to make me notice that the video and audio are not in sync.

    What should I do next?
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  6. I never suggested changing the tempo, certainly not yet.

    Is this a TV show? Commercial break cuts can account for runtime differences of several seconds.
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  7. Yes, spot on. This is an old TV show. The commercial break cuts surely makes it difficult to sync.
    What normally people do to make the Video and Audio sync in this situation?
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  8. See post #2 and let me know whether they actually drift out of time or if they just jump when there is an edit point.
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  9. What I see from the bar (shown by Audacity only when I play) and hear, I believe, that these audios are only drifting.

    Below I created from photoshop, so you can see that it basically is only few 0.x sec difference. But the difference increases slowly by time. And as you can see, Audio B (second graph) is around 4sec longer than Audio A.

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  10. Member
    Join Date
    Mar 2008
    United States
    Search Comp PM
    Can't you use the time stretch function to either shorten or lengthen the audio (what ever is required)
    while retaining the proper sample rate? First check a word or noise very close to the start and note it's time.
    get the two files to match as close as you can either by adding silence or deleting a little of the troublesome file.
    Then zoom to the end of the file and check a word or noise there and note the exact time. Re-time the file using the
    aforementioned time stretch so that the sound you heard at the end is at the same time stamp you found earlier..

    It's a manual process unfortunately, no magic wand or program to do it automatically for you.
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  11. davexnet, the time stretch function you that the "change tempo" effect on Audacity?
    I suspect the problem is because the tempo is not correct and maybe few milliseconds pause in the beginning. And my unfamiliarity with Audacity doesn't make things easier either.

    So in this case, I should make sure both begin at the same time, then do the time stretch (change tempo). Right?
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  12. Originally Posted by Chri5 View Post
    What I see from the bar (shown by Audacity only when I play)
    Not sure what you mean by this.

    Align them perfectly at the start by zooming in very close, then use the Time Shift Tool that is next to the Zoom button to move the entire track B to the left or right as required to match audio A. If you play them back together there should be no echo, only a strange "chorus" effect. If it begins to drift because of differing "tempo", echo will gradually creep in.
    Image Attached Thumbnails Click image for larger version

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