Hello, my question could be difficult to understand but I will try to explain. I should edit an audio file of 42 minutes (audio track from a movie). I have to retard or stop this audio file because at minute 24 it goes out of syncro, I tried to sync with vlc but the problem is that the audio goes out of sync at the middle and not at the beginning, so If I do with VLC it is ok at the first 23 minutes but after that it goes out sync anyway. There is a way to do that? Sorry for my bad english
That’s tricky…
You can try the [u]Change Speed Effect[/u].
You’ll need a video editor (or other tool) to re-combine the audio & video. Audacity is an audio editor and it can take the audio out of the video (you’ll probably need to install FFmpeg) but it can’t put it back.
And sometimes, just extracting and re-multiplexing (re-combining) the audio can cause it to go out-of-sync. I don’t know exactly what causes that, but it tends to be more of a problem with the more-compressed video formats (MPEG4, etc.). So, it may take several tries to get it fixed.
Do you think the drift is constant? That is, do you think it gets worse over time so you start to notice it half way through, then it gets worse by the end?
The tricky part is figuring-out how far off it is. If the drift is constant you can trim a some time off the beginning (or add silence to the beginning) until it’s in sync at the end. You should be able to do that with just your video editor. Then you can calculate the necessary speed change (which you’ll probably have to do with Audacity).
Sometimes, simply re-encoding with your video editor or with a free tool like [u]XMedia Recode[/u] will fix sync problems, but re-compressing may reduce the audio/video quality. (If you want to keep the same audio/video format you can just use a slightly-lower or slightly-higher bitrate.) …And sometimes editing or re-encoding the file will cause it to go out-of-sync.
Or, [u]Womble[/u] and [u]VideoRe-Do[/u] have tools to fix “time code errors” and sometimes that will fix sync problems. (These are not free.)