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Video at 24fps and Audio recorded at 23.98fps

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Soniya Chai
Video at 24fps and Audio recorded at 23.98fps
on Mar 22, 2019 at 4:35:46 am

Hi there,
I'm just starting on a project where the video was recorded at 24fps. Due to some miscommunication and a different production mixer one day, we have one day of audio recorded at 23.98 (48k), while all the other days were recorded at 24fps.

I'm cutting in Avid MC (2018.12.1) and wanted to know if I might run into any issues further down the line when I turn over to sound. I figured if I select 24fps in the dropdown menu in Avid when I'm importing the audio and sync using the slate/clap (we have reference audio with the video), there should be no problem moving forward. I tested this with a few clips and video and audio remain in sync throughout, even with longer clips.

I considered using WaveAgent to change the metadata on the audio files before importing but didn't want to go down that route if I didn't have to.

Appreciate any help or thoughts about this, thanks!


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Michael Phillips
Re: Video at 24fps and Audio recorded at 23.98fps
on Mar 23, 2019 at 1:42:50 am

Since there is no real frame rate for audio, it is more about 48kHz being sync with whatever frame rate the camera was running. In this case 24fps. When you import and select 24fps, it is calculating samples from midnight to create the timecode. So in this scenario, you will be in sync. Are you conforming audio in another application downstream? If so you will want to comment on those files and flag it as something to check if going back to original WAV files.


Michael


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Soniya Chai
Re: Video at 24fps and Audio recorded at 23.98fps
on Mar 23, 2019 at 2:25:27 am

Thanks for the response.

To your question, yes we will be conforming in ProTools further down the timeline and I was a little concerned about having issues with that since I noticed that the TC changes when I select 24fps in the dropdown menu in Avid (thank you for your explanation on why/how it does that). After reading your reply, I tested a few clips where I did not change the option to 24fps on import (for audio files), I left them at 23.98 and found that they sync up fine and remain in sync even over longer durations. This makes me think I can get away with not changing it while importing since this leaves the TC as is but again, just not sure if this might lead to complications further down the pipeline.


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Michael Phillips
Re: Video at 24fps and Audio recorded at 23.98fps
on Mar 23, 2019 at 1:58:56 pm

They will sync fine because of the 24fps video @48kHz recording. The issue may be downstream if Pro Tools is reconfirming from the original BWF files and uses the timecode/frame rate to find the offset in the file. That is when timecode may become an issue inside the BWF file. I would suggest opening those files in Wave Agent and changing the rate to match the other sources but do not have it recalculate the timecode. The timecode will be the same, but the metadata will be for the correct rate. Then import.

Michael


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Soniya Chai
Re: Video at 24fps and Audio recorded at 23.98fps
on Mar 23, 2019 at 5:22:52 pm

Thanks Michael. I used WaveAgent to change the info (without changing start TC) and will redo the import/syncing in Avid for the particular days with the mismatch.

Just out of curiosity, I looked at the metadata in Avid for TC on audio files brought into my Avid project (set up at 24fps) where I did not change the dropdown menu - as in I left it at 23.98 while importing, and the information here matches the files I brought in after adjusting the metadata in WaveAgent (23.98 -> 24). I'm assuming this is because my Avid project is at 24.


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Michael Phillips
Re: Video at 24fps and Audio recorded at 23.98fps
on Mar 23, 2019 at 5:42:29 pm

That's because Media Composer doesn't recalculate based on samples from midnight but rather a conversion at that timecode in the file. If you were to look at that file in Wave Agent and uncheck "preserve" timecode, you will see how it gets recalculated. That's why I'm recommending you make sure that all your BWF files are stamped with the correct rate so that Pro Tools or other downstream app doesn't interpret the way.


Michael


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Soniya Chai
Re: Video at 24fps and Audio recorded at 23.98fps
on Mar 24, 2019 at 7:40:44 pm

Makes sense, thanks again for the clear explanation. I went ahead with the WaveAgent adjustment and workflow :)


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