Is It Possible To Point Sync Audio To Video?

[LouieChuckyMerry]

Hello, and thanks in advance for any help . And apologies if this has been answered before; I searched about but found nothing useful. Some years ago when I began digitizing my DVDs and Blu-rays I botched several rips. Long story short, I've a handful of .mkvs where the audio is out of sync. Unfortunately the sync issue is neither constant nor progressive, such that a delay or speedup-slowdown would fix the problem. Instead, the audio is in sync at the beginning and end of the films and most out of sync in the middles; that is, they start in sync, gradually become out of sync, peak out of sync midway, then slowly resync until they're again synced at the end. All the audios and videos are the same length in minutes so I don't think it's a framerate issue. My question: is there any way to point sync the audio, like one can point sync subtitles in Subtitle Edit? If point syncing audio isn't possible, then does anybody have an idea of how to reverse whatever I did to the audios (it's been so long I can't remember what I did) given their characteristics (audio and video lengths the same, synced at beginning and end but not the middle)? Thanks again for any help.

[poisondeathray]

Rule out a playback problem first. Try a faster computer, try different players (e.g. mpchc, potplayer etc...)

If it really is in/out of sync you have to cut it up and sync the sections that are out of sync manually . Typically a video editor is used where you can see the audio waveform, realtime feedback, make adjustments

[LouieChuckyMerry]

Rule out a playback problem first. Try a faster computer, try different players (e.g. mpchc, potplayer etc...)

Thanks for the thought; I've tried multiple computers and players to no avail.

If it really is in/out of sync you have to cut it up and sync the sections that are out of sync manually . Typically a video editor is used where you can see the audio waveform, realtime feedback, make adjustments

That's the thing, it's not in and out of sync. It begins in sync, gets consistently more out of sync until it reaches peak-out-of-sync at the midpoint of the movie, then reverses course until it becomes in sync again at the end. If I made a graph of Sync vs Time, the first half would be a mirror image of the second half; that is, it would start at zero, the midpoint would be XXX milliseconds, then it would return to zero. Imagine an equilateral triangle sitting on a graph such that its left corner is at 0,0 and its top corner is the middle of the film, and its right corner is the end of the movie. Whatever is wrong is, for lack of a better term, symmetrical. That's why I'm hoping someone can recognize this characteristic and offer a reversal of whatever I did. Sorry if I confused you .

[poisondeathray]

That's the thing, it's not in and out of sync. It begins in sync, gets consistently more out of sync until it reaches peak-out-of-sync at the midpoint of the movie, then reverses course until it becomes in sync again at the end. If I made a graph of Sync vs Time, the first half would be a mirror image of the second half; that is, it would start at zero, the midpoint would be XXX milliseconds, then it would return to zero. Imagine an equilateral triangle sitting on a graph such that its left corner is at 0,0 and its top corner is the middle of the film, and its right corner is the end of the movie. Whatever is wrong is, for lack of a better term, symmetrical. That's why I'm hoping someone can recognize this characteristic and offer a reversal of whatever I did. Sorry if I confused you .

Theoretically , that's much easier to fix than multiple sync points. Conceptually, you only have 4 sections , the first "A" and last "D" don't count - they're already in sync ; so you just have to fiddle with the middle two , B,C.

You set your split points when it goes out of sync . Judging by the waveform and what's on the video. Obvious things like a car door slamming, would show up in the audio waveform very distinctly.

If it was truly symmetrical, then if you stretch by 1% and that fixes "B" , then shrinking by the same amount should fix "C". But usually these things are very finnicky. You have to make small adjustments, a lot of manual back and forth. Even if it "seems" like there are 4 sections, often there are more

[JVRaines]

It begins in sync, gets consistently more out of sync until it reaches peak-out-of-sync at the midpoint of the movie, then reverses course until it becomes in sync again at the end.

You can fix this by dividing the audio track at the point where the drift turns around, then changing the length of each part to restore sync.

[LouieChuckyMerry]

Theoretically , that's much easier to fix than multiple sync points. Conceptually, you only have 4 sections , the first "A" and last "D" don't count - they're already in sync ; so you just have to fiddle with the middle two , B,C.

I think I'm still not communicating very well. Technically, the only time the files are actually in sync are the first frame and the last frame; after the first frame the audio slowly begins to become out of sync until it reaches its most out-of-syncness at the middle of the movie, at which point this reverses and it slowly begins to become more in sync until it reaches the end of the film. Do you know of any freeware I could use to sync multiple segments without actually splitting the file?

[netmask56]

How did you rip your DVD's and BD discs. ie step by step method? As a trial you could re-rip a DVD using MakeMKV, this doesn't shrink the original size of the disc , more of this later if needed, but merely wraps the disc format in a MKV container as a single file. Do this and see if you are still having drifting sync

[LouieChuckyMerry]

How did you rip your DVD's and BD discs. ie step by step method? As a trial you could re-rip a DVD using MakeMKV, this doesn't shrink the original size of the disc , more of this later if needed, but merely wraps the disc format in a MKV container as a single file. Do this and see if you are still having drifting sync

When I began digitizing my discs I was so excited (and clueless) that I was mixing-and-matching audios and videos from different sources while using multiple programs. The few files I'm having trouble with are some of the first I ripped but it's been so long I don't remember exactly what I did, and all my discs are in storage in a different country. I'm now using MakeMKV, but in the past I've used AnyDVD, AutoGK, DVD Shrink, and BDHero, just to name a few.

Also, just to be clear, the sync doesn't drift. As I described earlier, the audios and videos are the same length so I don't think it's a framerate issue, and the lack of sync follows a pattern so it's not a matter of a simple, constant delay. Here's a crude example for a 100 minute long movie:

[poisondeathray]

Also, just to be clear, the sync doesn't drift. As I described earlier, the audios and videos are the same length so I don't think it's a framerate issue, and the lack of sync follows a pattern so it's not a matter of a simple, constant delay. Here's a crude example for a 100 minute long movie:


[Attachment 42311 - Click to enlarge]

Right, that's drift. All "drift" implies is progressively worsening audio desync with respect to picture (ie. not a constant offset). Anytime you have drift, it usually means A/V length mismatch. That's what you have, when you look at each section.

Think of it this way: if you have a progressively worsening +ms audio delay up to the inflection point, this means audio comes after the picture and is getting worse until that point, where it's most severe. If you were to cut the video right at that point - the matching audio would be too short and cut off. If you included the matching audio that corresponds to the full picture, it would be longer than the video. Thus you would need to "shrink" that 1st part so it matches.

It's exactly the reverse for the "2nd half" . At the inflection point, the audio is already + delayed compared to picture, but at the very end eventually becomes in sync. Thus, if you look at the "2nd half" and cut the picture - you have too much audio from the previous section. If you were to include only the audio corresponding to the picture for that half, it would be shorter than the video. Thus you "stretch" that part to match up.

Schematically it might look like this (exagerrated) illustration. The top is the video, bottom is the audio



If it was the opposite direction, then stretch the first, shrink the 2nd - the concept is the same.

You don't have to physically split the video . And it's not physically split into files, it's done on the GUI timeline which only references the actual audio & video . But you do have to divide up the audio to process in sections (I mean on the timeline) . I don't know of any good freeware NLE's that can do this type of work well, but this is what I was taking about in my earlier replies. You only have "2" sections - which I would consider good fortune instead of 100 little sections. You can try JVRaines' suggestion, but this type of work is usually done in a NLE, where you can "see" the video and manipulate audio at the same time on the fly