My end result videos have two audio tracks. One is from my action camera; the other from a digital recorder. I can put them together and sync them up but at time goes on, they become unsynced. For one example, I synced “claps” at 12 seconds into the video. Thirty-eight minutes later, they are five seconds apart. Suggestions?
Can you post a picture of the Properties menu for each footage from the action camera and the digital recorder? This way we can see the fps for the footage from each camera.
The video is 29.97 fps. The audio file doesn’t have a fps property.
The blue ios form the camera - a video file. The green is from a digital voice recorder.
Usually when this happens it’s because the speed of one of the files is faster or slower than it should be. Sometimes it can be seen reflected in the fps. What I would suggest is using the speed function in the Properties menu and changing the speed of one of them starting with low numbers until you match the speed it should be at. You’ll have to figure it out by simple trial and error.
Which one to change is something you’ll have to find out by listening to each audio and see if one of them sounds to you slower or faster than it should be.
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Thanks, I’ll give it a try. Neither one really sounds slower or faster than in should be. I guess I feel more comfortable messing with the audio file properties than the video file properties. Hopefully, once I get a factor to use, I’ll be able to use the same one in future projects.
The devices will have internal digital clocks running at a few MHz to drive the circuitry. These clocks aren’t precise and drift with temperature, therefore you have to sync the 2 clocks - this is known as genlcoking.
If you haven’t genlocked the devices, they’ll drift.
If you have, how are you genlocking the camera and audio recorder?
Either:
- Settings are wrong and the camera and audio recorder are free-running
- It’s using SMPTE LTC and isn’t re-clocking often enough.
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38 minutes is 2,280 seconds.
5 / 2280 = 0.002193 or 0.2193% drift rate
Try plugging that number into speed and pitch adjustments on the audio file.
Thank you all for the suggestions. For anyone else who is having the issue, using DRM’s suggestion (because it was the one I saw last time I checked in), here is what I did to sync up the audio from V1 and the audio from A1.
- Sync them as usual at the beginning of the clip.
- Locate a good place to sync toward the end of the clip. That means somewhere where the discrepancy is obvious an noticeable, like my second picture.
- Go into the Audio Properties | Speed.
- Change the speed of the audio in tiny increments until the two tracks match up. How tiny? Well in my 38 minute example, the factor was 0.997720.
So, @Austin, your calculation was pretty darn close! I’ll toss it in my notes.
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Sweet! For anyone else trying to follow the math, 1.000000x is normal playback speed. The audio was running faster than the video, and needed to be slowed down in this instance.
1.000000 normal playback - 0.002193 drift rate = 0.997807 predicted new playback speed
0.997720 was the actual new playback speed used by the OP. Since the prediction was based on a rounded “38 minutes” rather than accounting for exact seconds and frames, it was a little off.
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Glad to hear that you got it corrected! 
Just want to add that for this kind of an issue, you don’t need to do pitch correction. Since you’re correcting a distortion of the speed from the audio file your corrected file would now have the correct pitch. Pitch compensation is when you are altering the normal speed.
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