Audio is going out of sync

[Shasoosh]

I've used mkvmerge to get a mkv and a mp3 file in the same container. That worked out great but the audio was out of sync so I used the delay function in mkvmerge. The problem is that even if the audio is in sync at the beginning of the movie it will go out of syncpretty fast.
Something like a subtitle file with different fps. How can I fix that sort of thing?

Thanks

[Selur]

if your audio stream is synched against another video with a different frame rate using the stretch option might help,...
Not sure how this is related to Blu-ray ripping,...

[Shasoosh]

Oh, the original movie was ripped from a blu-ray. Mods can move the thread.
I tried learning about stretching but couldn't really understand what float divided in what float I need to enter there.

[Selur]

it's the multiplicative you stretch/shrink the audio length during playback.
iirc. it's targetFPS/sourceFPS (or the other way around; should be easy to test, I always forget which way it is )
in example if your mp3 is synced against a 25fps video stream, but should be added to a 24fps video stream the stretch factor would be 24/25 = 0.96. btw. this only helps if the frame count of the two steams video streams is the same, if one of them has different cuts/scenes this will not help,...

[Shasoosh]

Sounds like a great solution. Before reading it I tried something else that also worked. In mkvmerge I changes the FPS of the movie according to the target movie and used the delay. That worked great. Thanks!

[Selur]

yup, that solution should work too, unless you have multiple audio streams which are synced against different frame rates.
So keep the stretch factor somewhere in the back of your mind so that you will remember it if you encounter this problem with a source which has multiple audio streams.

[Shasoosh]

After a a few tries I ended up using the stretch. I did had a few audio streams an if I changed the FPS of the movie it would fix that specific audio stream but screwed everything else. Stretch working fine though. (btw, it's Target / Original, 25/23.976 in my case.. )

Thanks again!

[Selur]

No problem, happy to help.

A little warning about using stretch:
In general I would not recommend to use it to modify stuff the you want to reencode later, because most tools can't detect the stretch value from an existing file. (wrote code to do this in Hybrid, but I never say this in another tool)

Cu Selur

[Shasoosh]

I'll keep that in mind.
For some reason when I use the stretch the other audio stream are still some how effected. I don't know why. Everything should stay the same but other audio streams sounds really bad in some players and in other players, if I select an audio stream that I haven't modified in any way there will be no sound and the movie will run a lot faster.
Still trying to figure that out

Edit: In order to get better results I think I need to convert the file I want to take the audio from to 23.976.
What's the preferred way for me to change the original 25 FPS avi to 23.976 (or just the audio from there) ?

[Shasoosh]

Just a little update. After a LOT of tries and errors I've found that stretch sucks big time
It messes up the other audio streams if they are in different frame rate plus my streamer (a-210) will play the stretched audio stream with weird glitches and other audio weirdness. I ended up using meGUI to Encode the audio from the 25 FPS movie and add the delay and the change of frame rate from meGUI itself. The result is one mp3 \ ac3 I can add to MKVmerge with no extra config. It takes longer and a lot harder to sync but the end result is great for all audio streams.

[Selur]

Strange it should not mix up the synch of other streams (you stretched the audio not the video stream right?), but sure it does only help if the playback software/hardware understands the stretch-flag and does a decent job.

[Shasoosh]

Of course, I stretched just the audio stream that was 25 FPS. There's a good change that my streamer is the one to blame here although if I stretched one audio stream in every video player I've tried i got different results. Pot Player would play only the stretched audio, MKVplayer would play the stretched audio and when I select the non stretched stream the video will run in double the frame rate, VLC played them both but with glitches.

[Selur]

I use MPC-HC and it works fine.