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  1. Hello,

    Please can you help me?
    I'm trying to mux a video with two ac3 audio tracks using mkvtoolnix. One track is from another source. I was able to determine using Adobe's Audition that for the two tracks to be in sync I'll have to apply a 850ms negative delay to one (-850ms). I entered this value into mkvtoolmix's delay box, but the muxed mkv is out-of-sync. Mediainfo reports a positive delay by 14ms (-850÷32ms per frame = 26.5, so 27 frames x 32ms = 854ms-850ms=14ms).

    How do I solve my out-of-sync problem? Any help would be greatly appreciated.
    V
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  2. Originally Posted by vangeliis View Post
    I was able to determine using Adobe's Audition that for the two tracks to be in sync I'll have to apply a 850ms negative delay to one (-850ms).
    How? Seems like this is not correct.

    Is the delay constant throughout the movie or does it get progressively worse? Are the cuts of the movie the same (cinema, director's cut, (un)censored, ..)?
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  3. Hi sneaker,

    one track is from another source (foreign audio) but I'm positive the waveforms match when I apply a precise -850ms delay. Any clues?
    Thanks,
    V
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  4. Does MediaInfo show any delay for your original file? Is the original file actually in sync? How do you open your files in Audition? I think MKV is not natively supported by Audition. Are you extracting the AC3 tracks using e.g. mkvextract first?
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  5. No delay in the original file. I extract the first few minutes with ffmpeg into a container that Audition understands. Then I sync the waveforms and that gives me the delay. When the delay is positive it works very well, but when the delay is negative -as it happens in some cases, the muxed file is out-of-sync. Weird.
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  6. try with -1714 ms delay
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  7. Is the original file mkv or something else? Mkvtoolnix might work a bit differently depending on whether the input files are mkv, mp4 or ac3. Is the resulting file sync at the exact point where you "matched" the waveforms? As I said sync may get progressively worse over the course of a file. If you only look at the first few minutes you might not see it.

    Originally Posted by vangeliis View Post
    I extract the first few minutes with ffmpeg into a container that Audition understands.
    Try just to wav, i.e. like:
    Code:
    ffmpeg -i "original.mkv" -to 300 "original.wav"
    ffmpeg -i "other_file.mkv" -to 300 "other_file.wav"
    (-to 300 means only 300 seconds)
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  8. Originally Posted by ProWo View Post
    try with -1714 ms delay
    Please could you explain how you worked this out as I have other files with various delays to mux.
    Thanks.
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  9. @vangeliis can load the audio into 'UsEac3to' and apply the delay .. and we get the audio ready for remux ..

    In Output format->

    with ac3: %_.ac3 -864ms

    or

    with ac3-ffm: stdout.w64 -864ms | ffmpeg -i - -c:a ac3 -b:a 640k -center_mixlev 0.707 %_.ac3



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    Last edited by sekininsha; 12th Feb 2020 at 20:25.
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  10. I'm a Super Moderator johns0's Avatar
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    You can load the file into mpc-hc and use a time shift and see which value gives you the right sync,doing it this way requires no editing and you use the correct value mpc-hc gives you in your editor.
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  11. Thank you all for the very useful tips. I should have said I am on a Mac so most of these tools don't work. However I used IINA player to mux video and audio on the fly and to my surprise I had to apply a positive delay to the foreign track to get it in sync. So I went back in Audition and double checked whether I had mixed the tracks up, but I did not.

    How peculiar this is. Any clues as to why this is?
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  12. Originally Posted by vangeliis View Post
    Originally Posted by ProWo View Post
    try with -1714 ms delay
    Please could you explain how you worked this out as I have other files with various delays to mux.
    Thanks.
    Did it work?
    You said that -850ms delay gave a result of +14ms delay.
    So -850ms-14ms-850ms (desired) = -1714ms
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  13. Originally Posted by ProWo View Post
    Originally Posted by vangeliis View Post
    Originally Posted by ProWo View Post
    try with -1714 ms delay
    Please could you explain how you worked this out as I have other files with various delays to mux.
    Thanks.
    Did it work?
    You said that -850ms delay gave a result of +14ms delay.
    So -850ms-14ms-850ms (desired) = -1714ms
    Hi ProWo,

    It didn't. As it turned out I had to put in a positive delay to get the tracks in-sync. I don't understand why that is but there you go.
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  14. Originally Posted by vangeliis
    Hi ProWo,

    It didn't. As it turned out I had to put in a positive delay to get the tracks in-sync. I don't understand why that is but there you go.
    mkvtoolnix does not add negative delay, so for this the program 'remove' audio frames
    in your case 864ms (27x32) and then apply a positive delay of 14 ms.
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  15. Originally Posted by sekininsha View Post
    Originally Posted by vangeliis
    Hi ProWo,

    It didn't. As it turned out I had to put in a positive delay to get the tracks in-sync. I don't understand why that is but there you go.
    mkvtoolnix does not add negative delay, so for this the program 'remove' audio frames
    in your case 864ms (27x32) and then apply a positive delay of 14 ms.
    That's strange. With ffmpeg it's possible to mux audio track with negative delays.
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