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Old 30th May 2011, 11:34   #1  |  Link
mizumi
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audio and video 23.976fps to 25fps using mp4

I would like to know how to deal with a NTSC source I want to convert to PAL to synchronize it with a PAL audio track I want to add to it.

The video is mp4 (x264) and I use Avisynth & MeGUI for editing the video and Adobe Audition for the audio but I'm open to use other programs.

This is what I would do:
1. Convert the original NTSC source to 23.976fps using IVTC.
2. Convert the video from 23.976fps to 25fps using AssumeFPS("25") in avisynth or some other program? I used to use virtualdub's function but with mp4 it's not possible
3. I have to modify the audio lenght but don't know how to do it.

My doubts are these:
a) Do I convert the video from 23.976 to 25fps or leave it at 23.976fps?
b) Do I have to increase the lenght of the NTSC audio and modify the NTSC video from 23.976fps to 25fps? Or do I have to shorten the lenght of the PAL audio to be the same as the NTSC audio?
c) How do I the pitch correction in the voice when converting the audio?
d) In case I cannot do IVTC and have to leave the video at 29.97fps, how can I synchronize the original audio with the PAL track?
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Old 31st May 2011, 05:40   #2  |  Link
manono
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Why speed up the video to match the PAL audio? Me, I would (and often do) slow the audio to match the 23.976fps video. Convert the audio to WAV first. I slow it using BeSweet, although there are other ways. It will also adjust the pitch in the process. Then reencode the audio to whatever you want.

If the video is 29.97fps, then what you do depends on what kind of 29.97fps video it is (interlaced or standards converted), and how the audio was converted to 25fps, or if it was created at 25fps. A comparison of the 2 lengths should clue you in. They might even be exactly the same length and nothing has to be done.
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Old 7th June 2011, 20:34   #3  |  Link
mizumi
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Thank you, Manono.
I have this PAL audio which is shorter than the video I want to synchronize it with. The PAL audio is "21:15.960"
and the target video is film, and it audio is "22:21.415".

I have read that you need to convert the audio using a ratio of 104.271%, is that right? How would I do that using besweet?

The thing is I tried in Adobe Audition using the "stretch" effect with the 104.271% ratio and the PAL audio turned shorter instead of longer: 20:23.695.

So I looked for a solution and someone suggested using a 95.904 ratio. I wonder why this number as I had never seen it before (I did have seen 104.271%) but the thing is that the audio is now as long as the film audio.

Adobe Audition > Effects > Time/Pitch > Stretch:


The only settings I have edited these:
"Ratio" box: 95.904
Stretching mode > "Time stretch (preserves pitch)"

Last edited by mizumi; 7th June 2011 at 21:26.
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Old 7th June 2011, 21:37   #4  |  Link
manono
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Quote:
Originally Posted by mizumi View Post
I have read that you need to convert the audio using a ratio of 104.271%, is that right? How would I do that using besweet?
BeSweet has a PAL -> NTSC (25 to 23.976) preset you can use. eac3to can also stretch the audio.
Quote:
I wonder why this number as I had never seen it before (I did have seen 104.271%)
.95904 x 1.04271 = 1 (more or less). If the 1.04... number causes the audio to play even faster, then .95..,. will stretch it to NTSC length. It just depends on how the WAV editor handles it. Some do it one way, some the other.
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Old 7th June 2011, 21:39   #5  |  Link
setarip_old
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@mizumi

Hi!

It looks like Adobe Audition presents the RATIO (1:.95904) of stretching rather than the PERCENTAGE stretched (1.04271%)...

You'll notice that .95904 x 1.04271 = 100% or 1.0

OOPS - manono got there before I did ;>}
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Old 9th June 2011, 11:32   #6  |  Link
mizumi
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Thank you both for your answers. It was really helpful and I've managed to synchronize the audios wonderfully ^_^

Btw, Manono, I'll give besweet a go as it seems convinient, and see how it works!
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