Fix Audio Delays Permanently Using VLC & MKVToolNix

Multimedia files with ‘lip-sync’ issues are not so uncommon, although it happens very rarely in professional environments as they take extra precautions to avoid them.

In a previous post I wrote about how to fix some of these synchronization issues permanently using ‘Avidemux’, but since then I have received few complains of ‘Avidemux’ not being able to fix those issues in some cases. Now to be honest, I too have come across some of these problems but fortunately I have been able to fix them (so far).

‘Avidemux’ can do very little if the input file itself has some issues (corrupted video frames etc) but ‘Avidemux’ is also a bit buggy, so some of the blame goes toward it also. In any case, there are few other tools that you can try while trying to fix a sync ‘malfunction’, and ‘MKVToolNix’ is one among them.

An illustration :) ...
Illustration …

‘MKVToolNix’ is not an encoder as you can only use it to ‘extract’ audio/video/subtitle tracks from other containers (MP4, AVI, FLV etc) and put them into the powerful and open-source MKV container. While doing so this tools also lets you pass certain settings (sync, fps, aspect ratio …) and it is through that we can attempt to fix sync problems.

But please be aware that the only output format it support is MKV (and few of its variations such as ‘MKA’ for audio’, ‘MKS’ for subtitles etc) and unlike MP4 or AVI, MKV is not supported by a lot of commercial and strictly hardware based multimedia players. Computer users however do not have to worry about it as popular players (VLC, MPC, PotPlayer, SMPlayer, KMPlayer …) support it. Enough talking, let’s do it!.

Note: Make sure you have downloaded and installed the latest builds of ‘MKVToolNix’ from here. I also recommend that you use VLC because both these utilities are available for multiple operating system platforms, so you can use this ‘guide’ in any of them.

What we are going to do is …

*. First we are going to play the ‘troublesome’ file in VLC (or any other player that lets you change the sync temporarily) and we will try to identify the proper sync value.

*. Then we will simply enter that sync value into ‘MKVToolNix’ and save it as a new MKV file so that it is saved permanently. That is it!.

Step 1:

So open your ‘troublesome’ file in VLC, and let it play for a few seconds. Then simply press the ‘j’ key on your keyboard. This will make VLC play the audio track a bit ahead of the video. A single click increases the value by 50 milliseconds only, so unless the ‘gap’ is very small, you will have to press it a few times to get see its effect.

VLC with minus (ahead of video) audio sync value

Anyhow, if after pressing ‘j’ key for a few times it worsens the ‘gap’, then it is an indication that you actually have to make VLC play the audio track a bit behind (delay) the video. The shortcut key for that is ‘k’. Again, to feel its effect, you might have to press it a few times. If after doing that it seems to shorten the ‘gap’ then it is an indication that you are on the right track. So keep doing that until you come up with the perfect sync value.

VLC with a plus (delay) audio sync valueSo as a general rule, play with ‘j’ and ‘k’ keys, until you find the perfect sync value for that multimedia file. Once you have found it, simply take a note of it (note that depending on the file the value could be positive or a negative one. If it is a negative/minus one, then you should enter a minus sign before entering the value in ‘MKVToolNix’, more below) and close VLC.

Step 2:

Now open ‘MKVToolNix’ and load the ‘troublesome’ file into it. Then under ‘Tracks, chapters and tags’ field, select the audio stream/track (shown below is an example).

Selecting the audio track in 'MKVToolNix'

Step 3:

Then from under it, click on the ‘Format specific options’ tab and you will see an empty field that says ‘Delay (in ms)’. Now simply enter the sync value you found above into that field.

Entering an audio sync value manually in 'MKVToolNix'
Make sure to enter a minus sign (-) when needed (-200 for instance) …

Step 4:

Now click on the ‘Browse’ button under ‘Output filename’ field. Select a location and a file name for the output MKV file. Once done, simply click on the ‘Start muxing’ button. If everything goes without any errors, try playing the newly saved MKV file and now you should be able to enjoy it without any ‘lip-sync’ issues!. Good luck.

75 thoughts on “Fix Audio Delays Permanently Using VLC & MKVToolNix

  1. This only works if the sync is offset by a certain amount of time throughout the video. I’ve just recently played a video that was 1080P and started fine, but within 10 minutes it was lagging behind the audio (Audio would play then the lips would move a second later.) I hit K to make it match and it did after progressing it 200ms. Anyway, by the end (About 1.5 hours) it was at 3600ms. So yeah, I had to progressively step the delay of audio proportionally to the video throughout the entire movie.

    I’m no expert, by any means, but it possibly could have been due to a loss of a certain number of frames in the video. Such as every 30th frame was missing, for example.

    Anyway, thanks for the post.

    • Hi,

      It could be due to a frame-dropping which usually occurs if the the playback hardware cannot handle it, or, it could simply be due to wrong audio ‘time-codes’. For instance, if the encoder has tried to sync an audio track with a video that has a fps of 60 (for instance), but wrongly recognized the fps as 50 and has set the audio speed to match it, then as the playback progresses, a lip-sync issue can arise and it will get worse as you play into the track, although it plays perfectly well in the beginning.

      If you can however, figure out by how much the audio speed should be delayed or speed-up, then you can use the ‘Stretch’ option in ‘MKVToolNix’ to successfully fix it (I have fixed one in the past). To not to complicate things any further, you can use the below links for learning more and hopefully for attempting to fix it …

      • But the audio plays perfectly in the original file? Although, it has no index for me. I have to rebuild it in VLC all the time, which I don’t do I just play as is. Would this be the problem? even though the original still plays fine. Once used in Mkvmerge, it goes out of sync 10 minutes in then for the rest of the file.

        • Well, you can try the ‘Convert/Save’ feature of VLC. I’m not sure if it’ll fix the issue (since I don’t have a file with a corrupted index to test it), but once on the ‘Convert/Save’ page, add your file, again choose ‘Convert/Save’ button, and on the next page simply choose ‘Dump raw input’ and save your file.

  2. Thanks so much for this. I was having a sync problem with one of my recently converted videos and this simple guide helped me to fix it ASAP!

  3. Thank you for writing this article. The software works so well, super quick (takes less than a minute) and simple.
    BUT I found that I didn’t need to enter the time delay to fix the audio sync. The program fixed the sync itself, it detected the timecodes were wrong. Ex, my audio had to be synced 1.2 secs faster (-1200ms), but the resulting video had the audio at 2.4 seconds faster than the original. After ‘muxing’ the original file a few more times with and without my inputting the time delay, I found that the software initally fixed the sync on its own, then it further applied my manual correction.

    Conclusion, just drag and drop the original file into the input file and start muxing, no need to find the time delay on your own. Thanks again for the tutorial!!

  4. Hey man, thanks a ton, this was seriously helpful !
    Also I had a video which had a variable delay like for the 1st half (approx) it was -0.6 sec. & for the 2nd half (approx) it was -1.5 sec.
    Is there a way for this as MKVToolNix uniformly syncs the audio ?
    I was thinking to rather cut it [using video cutter/joiner] & then use MKVToolNix for audio sync.
    What u say man ?

    • Several people asked about fixing variable out-of-sync audio. I believe this can be corrected with the command-line tool mkvmerge using the -y (i.e. –sync) flag. If the command “mkvmerge -i bad.mkv” reveals track 1 as video and track 2 as audio, then the command “mkvmerge -o good.mkv -y 2:B/M bad.mkv” changes the timing of the audio track relative to the video track by applying the function f(t) = Mt + B (where time t is measured in milliseconds).

  5. You ROCK dude!!!
    I just ran into this problem with an mkv, and found your tutorial. That was the easiest video resync I have ever done!
    I’ve tried Avidemux for this, it never worked on anything other than avi.
    I’m a Linux user (Manjaro) and didn’t think it would be this easy using tools I have on my system and use all the time.
    Thanks SO much!


  7. What do I do with an MP4 video that plays perfectly on Windows 7 in any player I try but on XP in every player I’ve tried the audio starts out OK but gets progressively farther out of synch?

    The frame rate of the videos is for some reason 23.976. What’s up with that? They were digitally recorded for the web, not done on film or intended for TV broadcast. No reason to use an oddball rate like that.

    What can I do to these videos (without re-encoding) to firmly nail down the relationship between video and audio so they’ll play correctly no matter what operating system or player software is used?

    • I’m not exactly sure what the issue is Galane. Have you tried to play these files using the K-lite codec pack in Windows XP? The fps should not change unless you’ve changed it manually…

  8. Thanks bro for this help but I still have problem…
    I have a movie doenloaded in mkv format with dual audio… one of them has multiple delays… I mean.. sometimes audio comes too early.. then after 20-25 minute, the position changes.. then audio is late.. etc.. it goes on in full movie.. HELP

    • I’m sorry hritik, I don’t know how to deal with that. It sounds like a badly encoded multimedia file… You could however, try to extract the troublesome audio out of that file and put it to a different one. Then also save the remaining audio and the video file into a new .mkv file. Then later, merge both (the one containing the audio & the with both the other audio and the video file) into a new one. I don’t think it would help, but you can try it at least…

  9. You may try Avdshare VideoGo to add audio track to mp4,
    Working as an Audio Volume Booster, Avdshare VideoGo
    can easily Add auido to MP4 like add MP3 to MP4, WAV to MP4, M4A to MP4, AAC to MP4, FLAC to MP4, AC3 to MP4, etc.

    • Thank you. I’m actually aware of this application, but I didn’t mention it because it’s not free and it only supports the Windows platform (although one might be able to run it using Wine in GNU/Linux).

  10. this works, but it does not work for correcting specific parts only.

    if you adjust audio delays forwards or backwards, the entire track shifts.

    this method only works for movies that are out of sync for entire track

    gayan if you know partial edits, update your post

    • Hi Johnson,

      I understand your problem and yes I’ve come across such issues too. But unfortunately, you can’t fix those issues using this method as far as I know. Sorry about that.

  11. hi what if certain parts of the video are out of sync with different delays??
    for example at maybe 30mins the sound is delayed 1200ms but after i saved the file and went back to watching the video it suddenly has another delay at another later part of the video?
    or in the entire video only the audio in a certain time is delayed and the rest of the video is ok?

    • I don’t think it’s possible to fix that type of errors using this method. You may need the help of a video editor (something that’s a bit more powerful as well) to fix these errors.

  12. does this trick work on dual audio movies.I am having delayed audio not just in milliseconds but it comes after some minutes.Please help me out.

    • Hi,

      I think you’ll have to use some sort of a video editor to fix such issues. First you’ll have to ‘cut’ the portion where the sync issue starts, and then fix it and then re-merge the whole track.

  13. This guide was helpful and does work, but a heads up, unless I’m missing something it doesn’t work with the newest version of mkvtoolnix 9.9 and only works with versions 8.3 or older, as they’ve changed the UI and moved things around in newer versions.

  14. hi

    i didnt try this method and i dont know if i should. i used mkvmerge gui and then mkv2vob to convert my mkv, put it on my usb but when i try to play it on my ps3 it starts running fast and then it freezes. i can skip forward with the left stick but the same thing happens. any idea? i wanna copy it on my ps3 hard drive and watch it properly. i dont wanna stream it, convert it or lose the quality. can u help.thx

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