Fixing sound sync issues in a mkv file

[Psykro]

(I hope this is in the right category)

I have a mvk file where the audio and video are badly out of sync. Using MKVextractGUI I can separate the mkv video and aac audio streams.

What I need now is an app to be able to open these files, somehow reset the audio to be in sync with the video (which I'll probably have to do manually) and then redub as one mkv file.

Any suggestions.

[guns1inger]

Have you worked out what the sync difference is ? When you use mmg (MkvMergeGUI) it has an option to add a delay during muxing. This would save you having to re-encode. The field is on the Format Specific Options tab.

[Psykro]

aha ok i didnt know about that, will need to work out the difference.

thanks for the tip

[guns1inger]

I use Media Player Classic to determine sync delays. The number pad + and - keys shift the audio in 10 millisecond increments in real time.

[jmelendez18]

you can do the same with VLC. im pretty new to this forum, i have one question, i have some vids they are mkv file and the vid have english and japanese audio tracks, also english subtitles. how do i go on about fixing it? i know the audio delay is 1000 ms.
please help me if you can.
thanks in advance.
Jmelendez

[ConverterCrazy]

Hope this is not an old thread!

I got an MKV file where audio is advanced by 2500ms after about half the duration of the video.

I split the file at the duration after which the audio goes out of sync and then introduced the delay of 2500ms in the last part of the file with MKVMerge.
The audio was in almost perfect sync with lip-movements!

When I joined both parts, only the 1st part plays. When checked with MKVMerge, it displays both parts of audio and video as separate entities and not single audio and video files.

Then I tried Meteorite but to no avail.

How can I repair the file?

Thanks.

Note: I think if I played both parts of the file as video1.mkv and video2.mkv, the PotPlayer will play them seamlessly.

[AlanHK]

Take note of the exact time the sync changes.
MKVextractGUi to extract the audio file.
Open in Audacity and select from the discontinuity to the end, cut it, paste back in the same position (Just control-x, control-v) -- now the last segment is separate and you can slide it along 2500 ms.
Now just "Export" to the format of choice -- AAC is common for MKV. Use MKVmergeGUi to merge your new audio with the video from the original file.

[ConverterCrazy]

Thanks @AlanHK.

It's a 5.1 channel AC3 audio. Will Audacity be able to handle it at 448kB?

I don't like AAC format

[AlanHK]

Thanks @AlanHK.

It's a 5.1 channel AC3 audio. Will Audacity be able to handle it at 448kB?

I don't like AAC format

In that case, it might be better to use some AC3 tools.

#1st suggestion:
First you have already split the video into two videos?
Extract the audio from the second part (MKVExtract)
Use DelayCut to add a delay to the AC3.
Use MKVmergeGUI to replace the audio in the second video.
Check the sync.
Join the first part of the video to the new 2nd.
(MKVmerge append)

#2
If that doesn't work, can join the AC3 from part 1 with the delayed audio from part 2

command line:

copy /b file1.ac3+file2.ac3+file3.ac3 finalfilename.ac3

then mux this with the original video stream.

#2A
If that glitches, run the AC3 through Besliced.
"In order to fix a corrupted audio stream, simply drag it onto BeSliced window, and click on 'Fix File!'. On finish, BeSliced will pop-up a logfile that lists all errors that was detected in file."

I think Delaycut, with no delays, might also work to "clean" an AC3 file.

[hello_hello]

When I joined both parts, only the 1st part plays. When checked with MKVMerge, it displays both parts of audio and video as separate entities and not single audio and video files.

I've fixed the audio sync in MKVs exactly the way you're doing it on many occasions (splitting an MKV, adjusting the sync of one part, then joining them together again), but I'd guess when you tried to join the two halves with MKVMergeGUI you used the "Add" button instead of the "Append" button. You want to "Add" the first half, then "Append" the second half.

If you use a negative delay for the second half, MKVMergeGUI will trim the beginning of the audio accordingly when you save the second half as a new MKV. There's a slight chance after the two halves are joined there'll be an audible "glitch" where they're joined, but mostly it works fine. AC3 seems rarely to be a problem. Sometimes for MP3 there can be one.
If the second half requires a positive audio delay then after appending the two halves there'll be a slight gap in the audio. There's not much you can do about that, but having a gap in the audio has never caused me any playback problems.

[AlanHK]

Yes, try what hello_hello said first. I had assumed you were joining the videos correctly, but if you added instead of appended....

[ConverterCrazy]

First of all, my apologies to all you fine people for the delay in replying.

Incidentally it was my PC which kept getting hung whimsically.

Yes, hello_hello, I was being dang stupid - I didn't see the Append button in MKVMergeGUI - and was using Add instead! Well, GIGO, sort of.

This is what I did:

1. I split the file where audio went out of sync,

2. using the 2nd half, set delay of 2500ms for AC3 audio in Format specific tab of MKVMergeGUI

3. Remuxed

4. Used part1 and Appended part2 as you suggested in MKVMergeGUI.

Bingo!

Thanks @hello_hello and @AlanHK.

What would I do without forum.Videohelp.com and its very helping members.

[cottage]

I realize that this is an old thread but I've had the same issue and have another option to try for anyone else having this problem.

I've used the previous methods and they work but I've found the following easier:

I use VideoReDo. You have to buy the program but it's well worth it. It's not supposed to handle MKV files but it will resync these files in 1 ms increments live using a slider. Then you can resave the file in MKV format.
-load the MKV video (when looking for the file, you may have to click "all file formats" in the open file window)
-click "Tools/Adjust Audio" A window will open in the lower right with a slider that allows you to adjust the audio)
-when you are happy with the sync, simply save the new file (If you have no edits, it will ask if you want to remux the file. Do it. It's fast.)

Good Luck