Can't Sync 25FPS audio w/ 29.970 FPS video

Hhhh…Man oh man, this one here is driving me bonkers, guys. I know there has to be a way to do this, as I’ve seen people saying it could be done with Audacity. Been using it for 3 years now for a host of different things, but never had a use for syncing and FPS issues until now.

I am starting to think that one needs to be Euclid, Isaac Newton, Max Plank or Albert Einstein, because I have literally tried everything and this damn audio is just won’t sync up.

So here is the deal: When I lay the audio onto it it’s about 6 seconds out of sync. The audio is AHEAD of the video. Starts out fine in the beginning of course, but then the video falls behind. So, I thought it would be as easy as just delaying the audio by seconds which sometimes works just fine for some movies, some it won’t work…well, this is one of those that wont work. If I do that, the beginning is out of sync, but the 3/4 to end mark is just fine (face palm). Did a bunch of tinkering around with the stretching of the vid/audio for hours and nothing helps. Then I realized Audacity has much better tools for this.

The movie has a run time of 1:32:13.961 w/ a 29.970 framerate. The audio has a length of 1:32:07.488. You can clearly see the 6 second drift issue now based on those times. So I opened Audacity, went to the Change Tempo option, did the whole 1.198 tempo change that many were saying to do. That just won’t work, and when I mux the audio into the vid container and give it a go, the video is still behind by 6 seconds late into the movie. Uherr? Ok, so I then do a delay to the audio by 6 seconds and now it’s even worse than when I did that the first time. Just not getting it what the deal is. I did everything I was told to do by people who sure seemed to know their stuff with all of that.

Tried also to change the FPS of the video from 29 to 25 (in more a soft manner via an editor). All that accomplished was slowing it down too much into a quasi-slow motion effect. Did that initially AND with audacity after messing with the audio and no go again.

Searched the forums, found some people and admins talking about a lot of stuff that went right over my head, but got the gist of it with the whole Sliding Time Scale and using a 4.095 on the tempo setting. Really thought that would work after waiting 20 mins for it do its thing and nope. Yet again, out of sync by 6 seconds. I mean, how can this possibly be happening? It’s like something out of Lost when the whole time shifting thing was going on. I mean, I understand part of the problem is between the monitor and the chair too, as I am not expert at all with math, but good grief, how difficult can it be? :angry:

One thing I did notice though, is when I did the first Tempo change I previously mentioned, it drops the audio time by about a minute (shows it immediately at the bottom in the little graph before I export it). Well, that’s way too much. The difference is only 6 seconds, not a minute. It was even worse with the Sliding Scale, went down to 1:28 (just over 4 mins). Eeesh. I am sure the full audio was there, but that definitely explains a lot why it won’t properly sync. Funny thing is, when I hover over the vid file in explorer BEFORE making a 6 second delay, the time shows as 1:32:19 (this is without any Audacity usage). Then AFTER I do the 6 second delay (using MKVTOOLnix) it shows as 1:32:13. Yep, 6 seconds. I see that and get all excited, only to skip to the 3/4 mark and see that it’s out of sync yet again. Tried all of that again after doing everything I explained after using Audacity, and yeah, you guessed it, out of sync.

So can you guys please save me from having an aneurysm here, because I feel it’s about to happen as this driving me insane :laughing:

An hour movie in 25 and an hour movie in 29.97 both take an hour to go by. It’s only if you shoot the movie in one and try to project it in the other that you run into problems.

Audacity default sample rate is 44100 and video is 48000. Could you be crossing those by accident?

I wouldn’t use Effect > Change Tempo. I would use Effect > Change Speed. Change Speed has a control panel with several different ways to define the correction. It causes the least damage of the tools. In one of the ways you tell it the current duration and the desired duration.


Export the corrected track. Close Audacity. Open Audacity and open the track and it should be the corrected value.

Could you be having trouble with 29.97 > 30? I think the error is about one frame per minute. Get out your frame calculator.

1000/1001 is the conversion.


Which Audacity are you using? You can get 2.2.2 here.


Oh, wait. One more. You can have sample rate errors. Shoot the movie at 48000 and project it at 48001. The podcast people run into this. Everybody shoots their own voice and sends the finished, high quality voice file to a central editing location. There’s always somebody whose sound card is running off pitch slightly. That, too, is Change Speed.

Once you figure out what the errors are, they don’t change until the presenter changes computers.

And if you really offend the sound gods, you can get sync at the beginning and the middle but not the end. We call that broken, but you are still expected to produce a working show.


It’s bad practice to export the corrected work in the same file name as the original work—stepping on the old file. That’s just begging loudly for trouble.

You’re doing all this in WAV-Microsoft, right?


Let’s back-up a bit…

Exactly what are you trying to do?

Are you taking audio from a 25FPS movie and trying to sync it with the 29.97FPS movie? Are you trying to dub-in a different language?

Tried also to change the FPS of the video from 29 to 25 (in more a soft manner via an editor). All that accomplished was slowing it down too much into a quasi-slow motion effect. Did that initially AND with audacity after messing with the audio and no go again.

In general, your video editor should be able to convert between different frame rates/formats without changing playback speed. Maybe try a different video editor/converter.

If you want to change the audio/video format, try [u]XMedia Recode[/u]. It can do all kinds of conversions and I believe it can convert between NTSC and PAL.

You can get sync errors simply be editing a movie and this seems to be more common with the more-compressed formats. i.e. The MPEG-4 variations have more problems than MPEG-2, and sync problems are rare with uncompressed AVI.

I assume the sync issues are related to the time-codes imbedded in the MPEG formats but I don’t know what the root cause is.

Sometimes you can “fix” the file by recoding it to a less-compressed format (or sometimes re-encoding to the same format) before editing. If you can re-code it without introducing sync errors, you can usually edit it (including editing the audio separately) without problems.

Womble and VideoReDo (neither is free) have tools that can fix the embedded time codes without re-encoding the audio/video. Sometimes that helps, sometimes it doesn’t.

Worst case, you may have to cut the program into shorter sections to synchronize and then re-splice. That’s a tedious process since you won’t have a clapperboard to synchronize the sections.

Many times PAL (25FPS) is digitized by simply speeding-up the original 24FPS film. But that’s a 4% speed and pitch increase, which is worse than what you’re seeing.

It’s bad practice to export the corrected work in the same file name as the original work

I’m waiting for the answer to that one. At least one of those errors can be laid at the feet of not getting the change you thought you had by having the file > export process fail. And then using the “new and improved” file without checking.

In all cases you have a speed change. Both the pitch and duration. The musical pitch change is really tiny and you don’t notice it. There is no pure tempo change. To either get a tempo error or solve it, you have to rip the sound apart, reassign tonal values and put it back together again. No plain, simple video error can do that.

I assume somebody posted that Change Tempo seemed to work once and everybody piled on.

Also see: Audacity doesn’t have instructional videos. Most of the videos posted are incomplete, for an old version, misleading or wrong.


When I lay the audio onto it it’s about 6 seconds out of sync.

That’s as close as we get to the actual job. Flesh that out a bit. Which audio, what video? Where did the video come from that it has bad sound?

Yandex is in eastern Europe. How are things in Kazakhstan?