VirtualDub: Apply audio filters (time stretch) to a special range of video

[DerMoment1608]

Hello!

I have the following problem: I have a video file where video and audio are not synchronous. The problem is that the asynchrony gets more and more towards the end but it's no "linear growth" of the asynchrony, so using the time-stretch-filter for the whole video isn't an option.

But principally the time-stretch-functions seems what I need. I would only need to apply a different stretch to different parts. I've found out how to apply video filters only for a special range of the video, enabling blend and marking the part with curving editor. But I couldn't find anything like that while using audio filters. Is there any possibility to "say": "Use the time stretch of 1,0001 from frame 0 to frame 9958, time stretch of 1,0002 from frame 9958 to frame 18880, time stretch 1,0003 from 18880 to…."?

First splitting the video file into parts and saving everyone of them, then applying time stretch on every single part and saving again isn't a real option as the original file is 256 GB and this would mean I'd end up with around 768 GB hard disk space occupied for original file, split files and split files with time stretch, plus it would take ages with this much of re-saving.

[redwudz]

I've only had a similar problem when the video file was haphazardly pasted together.
And unfortunately, the only way to fix it was to chop it apart and fix the individual sections, then mux it back together.

But you could demux out the audio and split it into sections and just process them as the audio filesize might be a bit more manageable.
The problem would be locating where the various sync problems start and end on the video and reference that to the audio.

But one of our members may have a better idea.

And welcome to our forums.

[jagabo]

If you need a visual reference, make a small, highly compressed version of the video with the audio. Split that into parts. That will give you small files to work with. Make all your audio adjustments using those small clips. Join them all together. Demux the audio from the small clip and mux it with the final encoding of the large clip. Basically, proxy editing.

[DerMoment1608]

Thanks for your answers and the nice welcome

I did record an internet stream and the stream started to show the asynchrony :/ And I couldn't reload for not missing out a part.

I think I can't fix the audio separately as it it's mostly trying what time stretch is in time with the video, so I need video and audio at the same time to get the right stretching ratio. But I think I'll try the suggestion of jagabo, it does solve the problem with the huge video files and the long saving time (Edit: I could even only extract the Wav-Files and combine them after fixing the stretch in the small video parts)

[hello_hello]

Are you sure time stretching is the answer? I ask, because sometimes the audio can lose sync in "steps" rather than running at a different speed to the video, but if it happens in a few places the audio will still get more out of sync as the video progresses. If that happens then you'd find the first spot where the audio loses sync, slit the file there, find the next place, split it there, and so on..... then you'd apply an appropriate audio delay to each section (rather than stretching), save each as a new file, then join them all together again. It doesn't help with managing those large files, but I thought I'd suggest it as something to consider.

[DerMoment1608]

Are you sure time stretching is the answer? I ask, because sometimes the audio can lose sync in "steps" rather than running at a different speed to the video, but if it happens in a few places the audio will still get more out of sync as the video progresses. If that happens then you'd find the first spot where the audio loses sync, slit the file there, find the next place, split it there, and so on..... then you'd apply an appropriate audio delay to each section (rather than stretching), save each as a new file, then join them all together again. It doesn't help with managing those large files, but I thought I'd suggest it as something to consider.

Trying did show it wasn't I thought I could avoid "skips" at the points of cut with using time stretch that would have shown with just moving the audio. But then I had to realize the stretching in small parts needs to be much higher and the audio quality got bad. So in the end I did it with Movie Maker now, cutting the audio and moving the parts into the right position. With trying to cut in natural pauses the end-result isn't too bad now, much better than I thought.

Thanks everyone for trying to help and making me think in different directions