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  1. I have used FFMPEG and MKVTOOLNIX before but I know how to do the basics, cutting, muxing and extracting specific tracks or subtitles. What I want to do now is a bit different.

    I have one MKV file that has a video and audio track at 29.997 fps and I have a second MKV file that has a video and audio track at 23.847 fps. I want to keep the video and audio on the first MKV file with higher fps and mux the audio only from the second MKV file.

    But how can I go about doing this? Do I have to increase the fps of the second MKV file first?

    Code:
    ffmpeg -y -r 23.874 -i seeing_secondMKV.mkv -r 29.997 secondMKVFPS.mkv
    Or should I extract the audio and only increase it's fps? Or how?
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  2. Usually there is no speed difference between audio from a 23.976 fps source and audio from 29.97 fps source (conversion between them is done by telecine/inverse telecine). So first I would try to simply mux the 2 together and see if the output is sync. If it isn't try to find out if the sync gets progressively worse throughout the file or if there is a constant delay.

    ffmpeg:
    Code:
    ffmpeg -y -i "file_0.mkv" -i "file_1.mkv" -map 0 -map 1:a -c copy "output.mkv"
    or mkvmerge:
    Code:
    mkvmerge -o "output.mkv" "file_0.mkv" --no-video "file_1.mkv"

    The problem is we can't predict from these fps values how/if we need to convert between them to make them fit. For example the sources might be different cuts (cinema, director's cut, censored) and require more intricate solutions.
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  3. Originally Posted by sneaker View Post
    Usually there is no speed difference between audio from 23.976 and audio from 29.97 fps audio (conversion between them is done by telecine/inverse telecin). So first I would try to simply mux the 2 together and see if the files are still in sync. If they aren't try to find out if the speed gets progressively worse throughout the file or if there is a constant delay.

    ffmpeg:
    Code:
    ffmpeg -y -i "file_0.mkv" -i "file_1.mkv" -map 0 -map 1:a -c copy "output.mkv"
    or mkvmerge:
    Code:
    mkvmerge -o "output.mkv" "file_0.mkv" --no-video "file_1.mkv"
    The issue here is that I am getting two different audio durations. The difference is about a minute.
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  4. I don't care about duration. Is the audio sync with the video according to your eyes and ears?
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  5. Originally Posted by sneaker View Post
    I don't care about duration. Is the audio sync with the video according to your eyes and ears?
    no, there is a sync issue.
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