Hello there,
as i try to get familiar with audio syncing, i´ve come across several questions regarding how to start (as i´m sure there are different approaches) and seek help. So that i´m not getting used to a workflow which is fundamentally wrong.
The software i want to use is mostly freeware (audacity, eac3to; mkvtoolnx for merging video and audio but should there be a better way - as i´m sure there can be - i´m open to that)

I want to use a LPCM 2.0 track from my "La Haine" bluray and use it for the the UHD release of the movie (although it has a 2.0 DTS HD-MA track which seems to be the same audio - despite studio intro - just by looking at the two tracks in audacity, nevermind).
The UHD release is at 24 fps and my audio track comes from the bluray which is 23.976 fps. Both are 48 kHz

Now to my questions about syncing audio in general to understand the working concept (also for other projects):
1. Loading the audio track i want to use (from a older source or Laserdisc), one track from the new source into audacity and cut/add silence to the beginning of the old track to match the new track is the right way or do i have to do something different?

2. After editing a track, using eac3to to match it to the video source (if different fps) is also right?

3. Something i´ve come across while try to match different tracks in audacity: Even if the tracks have millisecond/sample-wise the same length, i hear a "hall/echo" effect while playing them simultaniously. Which means there not perfectly in sync?


BTW: Does anyone know (and have it) if the laserdisc audio from La Haine is the same audio track that´s found on the new UHD, just mastered to 2.0 DTS HD-MA?

I’m afraid it’s not just as simple as adjusting the start of the LD track to match the length of the audio you’re trying to sync it to.

I use Audacity too, I’ll get both tracks matched at the start with additional silence or a cut then let the tracks run. Once they go out of sync (the echo effect) I’ll stop the tracks and adjust the LD track to bring it back in sync. Normally this happens at a scene change so it can be done relatively easily. Some tracks only require a few adjustments, others need a lot more!

Let's first state a (not so) obvious fact: audio track from 29.97fps has the same speed of 23.976fps - that's because video has telecine.

Then; audio tracks from 24fps and 23.976fps have NOT the same speed! So, one should be slowed down, or the other should be speed up; which one is up to the user, but I'd always keep the lossy untouched - or slow down/speed up the lossless, that is the same; in case there are two (or more) lossless tracks, I'd go with 24fps to keep theatrical timing.

In any case you have tracks of only one out of two of this given speed, it's better to keep them as they are and change video fps - it will NOT re-encode video, but it's just a flag that says to the player which speed to play video.

So, answers to the questions:

1) first decide which speed the final project (audio+video+subs tracks) you want to get; then you have to change audio speed (if needed) BEFORE any edit; then you can cut/paste/delete/add anything
2) just select video fps in the muxer you use - like tsMuxeR or MKVtoolnix
3) is it possible to have 24fps and 23.976fps tracks of the same video, from different sources, at the same lenght - even if not very often; in that case, one has more (or the other has less) frames, hence audio of one track would be ahead/behind until it reaches the missing/added frames part, then will be behind/ahead. Or, simply, the tracks are a bit (or a lot) out of sync; you will notice it in particular during dialogue - different people hear different out of sync tracks, but usually it started to be noticed around 10/20ms, while is plain evident around 30/40ms for anyone; if it's just few ms, personally I'd not bother - unless you put it on sync at the beginning and it will stay put for the whole track, of course!
2)

(2021-10-05, 06:17 PM)alexpeden2000 Wrote: I’m afraid it’s not just as simple as adjusting the start of the LD track to match the length of the audio you’re trying to sync it to.

I use Audacity too, I’ll get both tracks matched at the start with additional silence or a cut then let the tracks run. Once they go out of sync (the echo effect) I’ll stop the tracks and adjust the LD track to bring it back in sync. Normally this happens at a scene change so it can be done relatively easily. Some tracks only require a few adjustments, others need a lot more!

Alright, so if i´m lucky i only have to add something to beginning and/or the end, but at other tracks i have to add/cut something in the middle of a track. If i misread your point, correct me.

(2021-10-05, 07:05 PM)spoRv Wrote: Let's first state a (not so) obvious fact: audio track from 29.97fps has the same speed of 23.976fps - that's because video has telecine....

So, answers to the questions:

1) first decide which speed the final project (audio+video+subs tracks) you want to get; then you have to change audio speed (if needed) BEFORE any edit; then you can cut/paste/delete/add anything
2) ....
3) ....

Thanks for the side facts regarding the telecine.

2) and 3) understood
1) i´m afraid i´ve to do more basic research, because i dont´t know how do i determine at which speed i want to/have to play a track - probably some equation. e.g. i decide to play the track i want to add at 100.4%. How do i know that percetage i´ve to add.

Still thank you for your informations, both of you.

(2021-10-06, 09:34 AM)SIUse Wrote: Alright, so if i´m lucky i only have to add something to beginning and/or the end, but at other tracks i have to add/cut something in the middle of a track. If i misread your point, correct me.

If you are syncing a Laserdisc track to a Blu-ray you will always need to make adjustments throughout the track as it will not be the same transfer. The only time you can manage with just a delay/cut at the start is if it is the exact same transfer (but maybe a different intro sequence) - for example when I synced the Caddyshack DVD Mono to the Blu-ray is just needed an adjustment at the start (as it's the same transfer as the Blu-ray). If it is a Laserdisc track you will need a lot more work - but it is usually worth the effort!

(2021-10-06, 09:34 AM)SIUse Wrote: 1) i´m afraid i´ve to do more basic research, because i dont´t know how do i determine at which speed i want to/have to play a track - probably some equation. e.g. i decide to play the track i want to add at 100.4%. How do i know that percetage i´ve to add.

WAIT! There is no 100.4%! PAL and NTSC difference is 4% (and not 0.4%) while 23.976 and 24fps is 0.1%.

So, try to change a track to 99.9% (or 100.1%) and see if they get in sync.

Test, test and, what I forgot? TEST! Trial&error method works (for me at least)

(2021-10-06, 11:43 AM)spoRv Wrote:

(2021-10-06, 09:34 AM)SIUse Wrote: 1) i´m afraid i´ve to do more basic research, because i dont´t know how do i determine at which speed i want to/have to play a track - probably some equation. e.g. i decide to play the track i want to add at 100.4%. How do i know that percetage i´ve to add.

WAIT! There is no 100.4%! PAL and NTSC difference is 4% (and not 0.4%) while 23.976 and 24fps is 0.1%.

So, try to change a track to 99.9% (or 100.1%) and see if they get in sync.

Test, test and, what I forgot? TEST! Trial&error method works (for me at least)

Ok, ok, ok^^ It was just an example figure, but i can see why it does have another meaning to you.
So, trial error. I nearly suspected that.

Thank you both

Best way I find is to get your two sources running at the same speed first, whichever way you want to do it. Then triple check that your laserdisc is in sync with it's audio.

Open two instances of Virtualdub2, put them side by side and open your laserdisc (plus audio - make sure your audio is uncompressed) in one and UHD in the other. Find a frame at the beginning you can use as a measure and adjust your laserdisc video, either by deleting frames or adding frames, until that frame you selected is the same frame number on both versions. You want to find a frame where there is a definitive difference between one shot and another, don't pick a scene where it's a fade. Quite often opening logos will be different between the two versions so you'll have to see how bad it is.

Once that's done jump forward 1000 frames on the laserdisc, find a good scene transition, note the frame number, go to that frame number on the UHD - is the transition at the same frame number on both? Good - jump forward another 1000 frames and do the same thing. Let's say it's now a frame out - you know there is a frame difference between frames 1000 and 2000. Go to 1500, are they aligned? If so the frame difference is between 1500 and 2000. Now try 1750 etc.

Eventually you'll find the particular frame, if it's an extra frame in the laserdisc you can cut out that frame, if it's an extra frame in the UHD you'll have to copy a frame from somewhere in the laserdisc video and paste it - just try and do it during a moment of silence if possible. Write down everything you do, along with the frame numbers and timestamps, so if something goes wrong you don't have to start from scratch.

Once you've finished and everything matches on both versions, select all on the Virtualdub with the laserdisc, then save the audio file. Load that into your editing software like audacity, go to the timestamps where you made changes and just double check everything sounds and looks ok.

It's worth noting that if your laserdisc source is running at 29.97 fps you'll need to deinterlace and decimate the video first, it won't alter the audio as spoRv says because 29.97 and 23.976 are the same, but your frame numbers will never match up.

(2021-10-14, 05:10 PM)alleycat Wrote: It's worth noting that if your laserdisc source is running at 29.97 fps you'll need to deinterlace and decimate the video first

Yep!

First deinterlace/decimate, then discard/add needed frames, then check audio in the discarded/added frames and you are done... a walk in the park!

It's much easier to sync in avisynth, import both sources (using frame accurate source filters) and stack them either horizontally or vertically. This way you're only working in one vdub window with one timeline