Question about syncing audio/video/subtitles

[mindblowing]

Hey folks! I apologize if this is the wrong category for this thread.

I have 2 Blu-ray releases of the same movie. They're different editions. The first one has better PQ, the second one has better AQ + more subtitles.

I used eac3to to extract the video track from the first disc, and the audio/subtitle tracks from the other, for the purpose of muxing them together into an .mkv.

Unfortunately, they don't share the same length. The video from disc #1 is 8 seconds longer than the video from disc #2. So the audio track and subtitles from disc #2 are running ahead of the picture.

I calculated the exact delay, and it's 7967 ms. I used mkvmergeGUI to apply the delay in question, but to my surprise the sync was still off for about half a second. I lowered it with 500ms - almost there! Finally, I set it to 7217 ms, which is 750 ms below the supposed "original", and I seem to have hit the spot.. but have I?

My question to you guys is how can I be sure that I've achieved the perfect sync? Surely there must be a better way of doing this, rather than relying on my own two eyes and guessing/assuming. Does anyone know of a certain software that can determine when/where there's a problem and apply such a fix for me?

Oh, if it's of any help, I think the delay is permanent throughout the whole movie. It seems to be 100% consistent. Can never be sure but, that's what I'm seeing.

Any tips would be gratefully appreciated! Thank you.

[awgie]

My question to you guys is how can I be sure that I've achieved the perfect sync? Surely there must be a better way of doing this, rather than relying on my own two eyes and guessing/assuming. Does anyone know of a certain software that can determine when/where there's a problem and apply such a fix for me?

"Perfect" is somewhat subjective. If it looks and sounds good to you - the viewer - then for your purposes that could be "perfect".

That being said, if you open the file in an editor (I use Vegas Movie Studio) where you can see the audio stream and the video image, you can align the audio more precisely. The easiest points at which to do it are where you can hear a loud noise (such as a gunshot) and you can see the action on-screen that makes the noise. Then you can simply shift the audio (or video) so the peaks in the audio are lined up with the image in the video.

[manono]

I do the same as awgie, except I use AviSynth for showing both video and audio waveform. Even though you'll never get it exact, you should be able to get it to within 20ms or so.

Does anyone know of a certain software that can determine when/where there's a problem and apply such a fix for me?

You seem to be asking for some sort of automatic fix and I know of no such thing.

[mindblowing]

@awgie @manono - Thanks guys, I will see to it. Meanwhile, if anyone has another suggestion. I was thinking, maybe I should apply the initial delay in eac3to, and not mkvmergeGUI. Does it matter where I do it?

[manono]

I was thinking, maybe I should apply the initial delay in eac3to, and not mkvmergeGUI. Does it matter where I do it?

You seem to be working under the assumption that the audio for both is the same length as the video for both. Therefore delaying the audio by the differences in length should bring it back in synch. But that's not always the case. There can be a delay in the audio in the original Blu-Rays. I'm not saying that's the case, but it's certainly a possibility. In addition, are you absolutely sure that after the initial 8 seconds the 2 versions are absolutely frame-for-frame identical? There are just too many variables here. In any event, to answer your question, as far as I know both programs will apply the delays in the same way and it shouldn't make any difference which you use. It wouldn't hurt to try, though. All you'll lose is some time.

[mindblowing]

I was thinking, maybe I should apply the initial delay in eac3to, and not mkvmergeGUI. Does it matter where I do it?

You seem to be working under the assumption that the audio for both is the same length as the video for both. Therefore delaying the audio by the differences in length should bring it back in synch. But that's not always the case. There can be a delay in the audio in the original Blu-Rays. I'm not saying that's the case, but it's certainly a possibility. In addition, are you absolutely sure that after the initial 8 seconds the 2 versions are absolutely frame-for-frame identical? There are just too many variables here. In any event, to answer your question, as far as I know both programs will apply the delays in the same way and it shouldn't make any difference which you use. It wouldn't hurt to try, though. All you'll lose is some time.

Thanks dude, I got everything working now. Big up! Thanks to all who chimed in!