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  1. Member
    Join Date
    May 2010
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    Dunedin, New Zealand
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    Hi all,
    Recently I muxed an 23.976fps video to audio that came from a 25fps video - to get the best quality.
    Problem is, after converting the video to 25fps(with mkvmerge) to match the audio, and matching up a time difference, they're still out of sync - I can match them at the start, but the audio gets more and more out of sync.
    I have no way to quantify this, so can't see how I can stretch it via mkvmerge as it requires numerical values of course.

    Does anyone know of an simple and easy to use application that uses a visual sync system such as the dual-screen visual sync system that Subtitle Edit uses?
    The audio is ac3 5.1, if that matters.

    Thanks in advance for any help,
    Simon
    Last edited by cinesimon; 5th Sep 2011 at 20:44.
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  2. Member
    Join Date
    Feb 2004
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    Australia
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    More out of sync is correct ... then don't change the video's fps.

    Use audacity > effect > change speed ... - values stretches ... you only need to calculate the % difference between video and audio.
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  3. Member AlanHK's Avatar
    Join Date
    Apr 2006
    Location
    Hong Kong
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    I'd use Audacity:
    Load both audio tracks.
    Use the "change tempo" effect to stretch/compress the new audio so it matches the original.

    Delete the original track, save the new one as AC3, MP3 or whatever and mux it in.
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  4. Originally Posted by cinesimon View Post
    I can match them at the start, but the audio gets more and more out of sync.
    I have no way to quantify this
    Sure you do. Determine how far out of sync the two are near the end of the video and calculate a ratio. For example, if the video is 3600 seconds long and the audio is 15 seconds ahead of the video near the end, then you have make the audio 3600 / (3600-15) longer -- 1.004184.
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