Audio sync points - is there such a thing?

[shasoosh]

Here's my problem. I'm starting a project where I want to sync an audio stream from a.avi (mp3 or ac3) to a video file, b.mkv for that matter. the video content is identical (credits aside)
a.avi is 25FPS
b.mkv is 23.976FPS

This is what is giving me the best result yet:
I'm converting a.avi to a.mp3 with 23.976 frames using meGUI. (I suspect that meGUI isn't giving me perfect results but I'm not sure)
Then I'm using MKVMerge to mux those two and maybe giving it a bit of delay as needed. The problem is that it's not perfect. I don't know what causing it but even if the sync is 100% accurate at the beginning of the movie, somewhere along the middle the audio will be half a second - 1 second out of sync.
I know that with subtitles you can set syncing points, is there something like that for audio?
Can you think of anything else that might help me out?

Thanks

[tebasuna51]

- You must be sure than the avi and mkv video are identical, frame to frame (ignoring initial and final credits).
The initial credits difference can be solved with a initial delay, the final credits difference can be ignored.

- If avi video 25 fps and audio are in sync the converted avi audio (25 -> 23.976) must be in sync with mkv 23.976 video.
Can have some inacuracy but never 1 second.

Please explain the method to convert audio (decoder and AviSynth option). Put the MeGUI log.
Please be sure than videos are identical frame to frame.

[Asmodian]

Each subtitle just has a start and an end time, not really a sync point.

You cannot do something like sync points for audio because if you adjusted the audio at the sync point it would be very noticeable as some sort of discontinuity.

I have noticed that really often different sources of what should be the same video will have a slightly different total number of frames or run times. I don't know if it is because of slightly different edits or a slightly slow/fast transfer or what happened but I often run into this. I have even had situations where it is pretty much synced at the start and the end but it is off in the middle. I think the people mastering different editions do not care about keeping every frame or using exactly the same run times, they just want their edition to be watchable.

If you are lucky you might just need to use a ratio slightly off of 25/23.976. If the two videos really are frame by frame identical ignore me. :o

[Maccara]

You cannot do something like sync points for audio because if you adjusted the audio at the sync point it would be very noticeable as some sort of discontinuity.


One way to avoid discontinuities would be manually handling the audio in sections and stretch/squeeze to "sync points" as necessary.

Tedious, to say the least, if there's a lot to sync. Don't know of any automated way to do it.