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I have an MKV (an Italian version). I have extracted the H264 and the unwanted (Italian) AC3 audio. Now, I'd like to remux it with an English audio track (I have).

The problem is, the English track is quite long (around 1 hr. 50 mins or so...) while the H264 track is 4 mins behind. Is there a way I can reduce the duration of the audio (by some approximation) so that I can resync with the track and mux it into MKV container?

Actually, the audio delay at different positions made me suspect that the rate of AC3 track is quite fast (relative to the H264 track). And now, with mkvmerge, I changed the FPS to the default 24000/1001p and finally, it synced with the audio. Now, it's playing perfect...

share|improve this question
You extracted the audio from an MKV already, so why would you just ignore that? Have a look at the delay for that track in the original MKV file, and set the appropriate value when you're remuxing (yes, MKV has this built-in, which is why the tracks were unequal length but played back fine to begin with). – Breakthrough Jun 12 '13 at 20:26
@Breakthrough: You seem to be suggesting that the MKV contained both audio tracks, whereas nothing in the question suggests that's the case. Also see Bon Gart's answer below which covers the possibilities, given the English track came from elsewhere. – Karan Jun 12 '13 at 23:03

The problem is where exactly is that extra length? Is it in the beginning? Is it at the end? Is it in some portion of the movie that is different? You know... does the English version of the film have a 4 minute scene that the Italian version doesn't? Or, are there multiple different scenes between them (for example... the differences in all the releases of Macross Plus).

Unfortunately, you really can't just chop those 4 minutes off one end or another, and expect the audio to sync up. What you are most likely going to have to do, is take an editor, examine the audio with the video, find where the differences are, and then decide. If it is an extra scene, then you will have to edit that portion of the audio out. If it is just some kind of speed difference (the audio track has been slowed), you may be able to resync it.

This is a link to a search at which is a site that WILL become your friend in this endeavor. There you will be introduced to a variety of tools to do ALL of these kinds of things (edit the audio track, replace the track in the MKV, resync the track, etc.) Read through a few of the threads in the search, and grab some of the tools. The site also provides multiple tutorials in how to use the tools that they suggest.

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Truly speaking, all my extractors & muxers are actually from that site. I watched the video somewhat (not completely). And, gone crazy by the long duration. So, I thought the bitrate of audio might have been increased or something like that. Okay, I'll definitely try listening to both carefully ;-) – Waffle's Crazy Peanut Jun 12 '13 at 20:36
Not just extra scenes, there's also the possibility that the audio and video tracks came from NTSC/PAL copies or vice versa, which would also cause a sync issue. – Karan Jun 12 '13 at 23:06
@Karan Absolutely. My impression from the question is that the English audio did not come from the MKV container, but from a different source, which is why my answer is phrased as such. If the original was PAL, and the English was NTSC, that would support your hypothesis. – Bon Gart Jun 13 '13 at 1:46
Thanks for your answer. But, a slight change in the FPS solved it. Have a look at my revision Bon. If you can address it, I'll be happy to accept your answer ;-) – Waffle's Crazy Peanut Jun 14 '13 at 10:28
@ϚѓăʑɏβµԂԃϔ actually, since you discovered what the actual problem and solution was, you should post that as an answer yourself. Answering your own questions is allowed here. Just detail how you used MKVMerge to do it, as well as where you can download it from. – Bon Gart Jun 14 '13 at 10:35

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