Audio out of sync when converting from MKV

[carlmart]

Today I had another (rare) case of audio being off sync when converting from an MKV file.

The original file was in perfect sync; when converted got off by about 100ms. I had to readjust it in DLP and went fine, but I wonder what is it that makes sync drift.

[Baldrick]

The mkv container may contain a time delay that the converter ignores...or it could be anything like corrupt video/audio, etc.

But it would also would be good to know exactly HOW and what tools you are using...

[carlmart]

The mkv container may contain a time delay that the converter ignores...or it could be anything like corrupt video/audio, etc.

But it would also would be good to know exactly HOW and what tools you are using...

I am using two tools: MKVextractGUI to demux the file and avisynth to convert it to m2v.

In this case I splitted the file in two discs, so I had to process the audio with avisynth too, using "soundout". But I did this several times and never had sync off when splitting.

BTW: the delay was 200ms instead of 100ms. Unfortunately I was in ahurry to finish the job, so I burnt three DVDs until I got it right, as I though it was 100ms at first, and then 300ms. Now it's fine. I imagine the second disc will have the same drift, but I haven't checked that yet.

Update: the second disk had to be delay corrected too, same amount.

But I wish there was a better, more precise way to do so. Like loading video & audio on a timeline and moving things until precisely on sync. Any suggestions on how to do that? Someone suggested to me the Vegas editor, that seems to accept m2v files. Can anyone confirm on that?

[maxrockpro]

Even I have a similar issue with one of my videos. The original video file(.mkv) has time delay that fixes the sync issue. But, Im unable to play it on my Sony HT and also directly on my LG HDTV. Sony just skips the file and LG says the file is invalid. Video re-coding with Xmedia Recode and Avidemux result in out-of-sync files. I do not want to change the video or audio format, just want to re-code the video file to make it playable on standalone media players.

[carlmart]

First of all you should extract the audio with MKVextract. Some players refuse to play mkv files with PCM audio or any other but Dolby or DTS.

If it's not any of the latter, then you could convert the audio track to one of them.

The sync issue might be corrected when remuxing with MKVmerge, by using delay. Try that and see what happens.

[hello_hello]

If memory serves me correctly....

If you open the MKV using MKVCleaver you can use it to extract the audio the same way MKVExtractGUI does (well I've never used MKVExtractGUI). MKVCleaver also has an option to extract the timecodes, which it'll extract to a text file. If you extract the audio timecodes and the first value isn't zero, then the first value is probably the amount of audio delay you need to apply. At least that's how I remember it....
If I'm correct it only applies to a positive delay amount. If you're needing to apply a negative delay then there's some other problem.

Sometimes I convert MKVs to AVI and for no apparent reason I can find, I'll need to apply an audio delay to the AVI to put it in sync. Even though they both seem to have the same number of frames etc and the encoded audio and the original are the same lengths. Mostly I've given up trying to work out why as it doesn't happen very often and just does my head in trying. To work out how much delay to apply though.....

I open both the original and encoded files using two instances of MPC-HC (I think when running two instances you need to pause both videos while applying a delay or it won't work, and the audio is delayed by tapping the + and - keys). Anyway I run them both and quickly pause and restart one of them until the audio of the two videos is perfectly in sync. You can tell when it's in sync because it'll produce a "phasing" type of effect. Then I watch for scene changes. If both videos change scenes at exactly the same time then the audio sync for both videos is identical. If they don't I pause them, adjust the delay of the encoded video a bit and go through the process again. Once the scene changes happen at exactly the same time while the audio of both is in sync, I use the amount of delay displayed in the MPC-HC status bar to apply a permanent delay to the encoded video. If there's no other way to determine the amount of delay required, that's the only method I've found for getting it correct, but because your eyes can see very minor differences in scene changes between two videos, it allows you to get the delay correct down to about +-10ms.

[maxrockpro]

The new Sony, LG and other standalone or integrated media players do support .mkv with AC3, DTS etc. fully. My issue is with any file that has time delay resulting in some error on these players. The files play fine on my PC.

[maxrockpro]

The new Sony, LG and other standalone or integrated media players do support .mkv with AC3, DTS etc. fully. My issue is with any file that has time delay resulting in some error on these players. The files play fine on my PC.

Latest Xmedia Recode versions recognize the time delay and re-encode videos accurately in sync.

[Selur]

woudnd't it be better/easier to simple demux the audio and fix the delay in the audio stream either through delayCut or by reencoding it, rather than reencoding the video stream?