Latest post Sat, Mar 8 2014 11:51 PM by S.Clements. 6 replies.
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  • Sat, Mar 8 2014 9:16 PM

    • S.Clements
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    24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    Hi,

     

         I have a bit of a problem.  I have footage that was shot at 24 fps that needs to go into a 25 fps sequence.  I don't want to use frame interpolation, so I used apple cinema tools to speed up the 24ps footage to 25fps.  This means that the audio must be sped up as well.  I read in the forums that the audio needed to be sped up by 4%, so I tried using the program Wave Agent to convert the sound to 45864 Hz and then I imported it into Avid at 48000 Hz.  Unfortunately the sound drifts out of sync.  Does anyone have any ideas for how I can make this sound sync up with the sped up picture?  Many thanks.

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  • Sat, Mar 8 2014 9:52 PM In reply to

    Re: 24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    Your math is off. If you stamp the sample rate to 50,000Hz <(25/24)*48000>, that would speed up the sound. So use Wave Agent to stamp at 50KHz, forcing speedup upon playback. Import into MC with S/R conversion to 48KHz. Should then sync up to the image you sped up to 25fps. Do double check if the 24p is true 24.000fps or 23.976fps. The latter is sometimes referred to as 24p as well.

     

    Also, the slowdown number would be 46,080Hz <(24/25)*48000>.

     

    Also see: http://www.jobterburg.nl/Publications/TVScenes_25_24.pdf

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  • Sat, Mar 8 2014 10:16 PM In reply to

    • S.Clements
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    Re: 24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    Job ter Burg:

    use Wave Agent to stamp at 50KHz, forcing speedup upon playback. Import into MC with S/R conversion to 48KHz. 

    Also see: http://www.jobterburg.nl/Publications/TVScenes_25_24.pdf

    Hi, Job.  Thanks for your help.  I was trying to reverse engineer your article on this.  Unfortunately the 50,000 Hz stamp put things wildly out of sync in Avid.  This is because the separate sound was recorded at 44.1kHz, I believe.  I have tried speeding that up by 4.167% and that gets pretty darned close, but it's still not perfect.  There is a wee bit of lip sync drift.

    Avid Media Composer 8.3.1 Macbook Pro (Retina, 15-inch, Mid 2014) 2.8 GHz Intel Core i7, 16GB Ram Mac, OS 10.10.2 [view my complete system specs]
  • Sat, Mar 8 2014 10:21 PM In reply to

    Re: 24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    S.Clements:
    sound was recorded at 44.1kHz, I believe

    Well, you'd need to make sure. Then the math would be (25/24)*44100=45937.5. That's a bit tricky, as you can't add fractions as sample rates in Wave Agent. Would probably be better to convert to 48.000Hz first, then pull up to 50K, then import into MC.

     

    Also DEselect 'ignore pulldown and pull-up rates' when importing, just to make sure you are actually converting the pulled up source.

     

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  • Sat, Mar 8 2014 10:37 PM In reply to

    • S.Clements
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    Re: 24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    Job ter Burg:

    better to convert to 48.000Hz first, then pull up to 50K, then import into MC.

    Thanks so much for your help, Job.  When I convert the 44.1 kHz to 48 kHz in wave agent first and then convert to 50 kHz and bring into Avid, it's way too fast and out of sync.  

    For some reason, this works.... I convert the 44.1 file to 48 kHz in Adobe Media Encoder - that program doesn't adjust the speed??? whereas Wave Agent does???  Then, I convert that file to 50 kHz and bring into Avid and that seems to be fine.  

     

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  • Sat, Mar 8 2014 10:50 PM In reply to

    Re: 24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    The difference is: if you do a sample rate convert (like in MC or AME), the speed is not changed, but the sample rate is. The duration of every 44100 samples (lasting one exact second) is redistributed over 48000 samples (still lasting one exact second).

    When you use Wave Agent, you are not converting the file at all, you are just adjust the playback clock for the file, cheating it to a higher rate, which will increase the speed. So rather than 48000 samples played back in one exact second, 50000 of the originally recorded samples are played back in one exact second. Once you import this into MC, these 50000 samples (now lastig one exact second) are redistributed across 48000 samples (stiil asting one exact second).

    So what you desribe having done is exactly what I meant. First redistribute (sample rate convert) so your source becomes 48K, then pull up to 50K (restamp the clock metadata), then import (with sample rate conversion) into MC.

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  • Sat, Mar 8 2014 11:51 PM In reply to

    • S.Clements
    • Top 150 Contributor
    • Joined on Sun, Jul 3 2011
    • London, United Kingdom
    • Posts 811
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    Re: 24fps footage in a 25fps sequence with separate audio recorded at 44.1 kHz?

    Great!  Thanks for the explanation, Job!

    Avid Media Composer 8.3.1 Macbook Pro (Retina, 15-inch, Mid 2014) 2.8 GHz Intel Core i7, 16GB Ram Mac, OS 10.10.2 [view my complete system specs]
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