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  1. Member
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    Having encoded a VOB index file i now need to mux the original audio back to the outputted MP4 video. I deinterlaced with QTGMC so now have 50fps for smoother playback as opposed to 25p which will just make the video look choppy since it isnt interlaced anymore. Is there any good MP4 muxers that mux up the audio to match the framerate of the videp, as using one i notice the video a little out of sync, maybe by micro seconds and it only lets you choose upto 30fps audio.
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  2. Audio doesn't have a framerate. However, since your 50fps video is the same length as your original 25fps video, you can use the same audio without having to stretch it (or, its original 25fps framerate). If it's out-of-synch, maybe you just have to add a delay.
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  3. You can try ffmpeg as muxer - agree with manono - if video duration is equal to audio duration then you should have perfect synchronization - side to this for sure this is not about microseconds - a/v synchronization is probably somewhere in area of few tens/hundred milliseconds.
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  4. Member
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    I decoded the VOB files using DGIndex and noticed it has delayed the AC3 file by 9ms as the filename says "VTS_03_1 T80 2_0ch 192Kbps DELAY -9ms" But the audio is still the same length as the video, so i'm confused lol.

    I never knew ffmpeg had a muxer option, maybe it would sync up properly then if it's being encoded with the video. Having played back the original VOB too and other files, has the same issue, maybe i'm reading too much into it or it's a problem with the media players. Would the 9ms delay make things ever so slightly off?
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  5. Member Cornucopia's Avatar
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    Think of the math:
    If you have a 50fps video, each frame lasts 1/50th of a second, right?
    1/50 = 0.02 sec. Or 20msec.
    So a shift of 9ms is less than half the duration of even one frame. NOT something you would ever even notice as out of sync (unless you were one of those rare individuals sensitive to such things).

    Scott
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  6. Originally Posted by Master Tape View Post
    I decoded the VOB files using DGIndex and noticed it has delayed the AC3 file by 9ms as the filename says "VTS_03_1 T80 2_0ch 192Kbps DELAY -9ms" But the audio is still the same length as the video, so i'm confused lol.

    I never knew ffmpeg had a muxer option, maybe it would sync up properly then if it's being encoded with the video. Having played back the original VOB too and other files, has the same issue, maybe i'm reading too much into it or it's a problem with the media players. Would the 9ms delay make things ever so slightly off?
    No worry -9ms is to compensate packet distribution across file - thanks to this some packets are loaded to buffer and they are presented (i.e. they are visible/audible) in proper relation. It is proven (for example by Dolby) that human are insensitive even for 50 - 100ms difference - very strict certification (such as Dolby) require sync to be within -20ms and +60ms (for example) so with -9ms you are on very safe side.
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