Frame rate from audio 24fps to audio 23,976

Hi, I have a problem with video synchronization. I would like the audio which is 24,000 fps slowed down to 23,976. I tried from one topic from this forum however it did not work. So I am refreshing the question for others and myself

I tried from one topic from this forum however it did not work.

And that topic was…?

The basic NTSC converstion is 1000/1001. Multiply whatever that calculation comes out to times 24 and it gives 23.9760239…etc. It intentionally never comes out exactly even. That was the math needed to keep the color information in US TV broadcasting from colliding with the sound and interfering (too badly) with the scan lines.

If I had to guess at it, I would say Audacity can’t do math with that kind of accuracy.

You are using Effect > Change Speed, right? What happened when you put the two lengths of the shows in?


I marked all 6 tracks, gave the velocity multiplier to 0.999 and also 1.001. Then I aligned the original audio to the reworked one and the timeline was not perfect. But I tried to align it anyway after alignment and so every few minutes, the audio desynchronized.

I marked all 6 tracks

OK, so right away you’re not doing a simple speed change job. What’s the actual job?

Which was the topic you couldn’t get to work?

Are you using Effect > Change Speed?

It’s easy to miscalculate the resources Audacity needs for a job. When Audacity imports a sound track, it converts it to a super high quality format so as not to create damage during effects and corrections. So right away, it’s bigger than you think.

During some jobs, Audacity will create a backup by making an exact copy of the whole show. Some effects just take a lot of calculation and math processing and that needs room, too. I bet that resync error is your computer running out of resources or room.

What would happen if you created speed corrected WAV tracks one at a time and then imported them into one large show? What happens if you used the tool where you entered the length of the tracks instead of trying to do the detailed math?


You might have to figure-out the actual correction factor yourself. Sometimes the audio & video can go out-of-sync simply by editing and this seems to be worse with the more-compressed formats (like MPEG-4, etc.) But I’ve also had it happen with MPEG-2.

Is there a chance that the file is PAL (25fps)? Film to PAL is usually just a simple speed-up so the PAL version of the movie has a shorter playing time and the audio has a higher pitch.

And/or it might require some trial-and-error, especially if you can’t find something to use like a clapperboard to find the sync error in the beginning and at (or near) the end.