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Major Issue! Syncing video with foreign audio takes.

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Steven Probets
Major Issue! Syncing video with foreign audio takes.
on Aug 9, 2011 at 7:01:11 pm

I have been asked to sync a 24fps video with 5.1 audio which needs dubbing over. It has been properly mixed and I am setting the correct settings in FCP for 5.1 auido to be converted to stereo (see my previosu post). The clips are marked as 23.98fps audi clips - which tells me they were mixed with the video and outputted with the video at 23.98fps.

On my output the audio slowly becomes out of sync and I guess this is the issue - 24fps source video with syncing to 23.98fps audio (well audio extracted from the language dubbing mixdown at 23.98fps).

If this is the issue is there anyway around this to sync it up? I cannot really stretch the audio as it is an expodential speed change. Will I have to convert the 24 frame footage to 23.98? If so, what is the best way of doing this?

Thanks in advance.


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Jean-Christophe Boulay
Re: Major Issue! Syncing video with foreign audio takes.
on Aug 9, 2011 at 8:03:45 pm

Hi Steven,

Audio does not have frames per second. It has samples per second, in most cases concerning audio for video, either 44100 per second or 48000 per second, a.k.a. 44.1kHz and 48kHz.

The first major error people do with audio is not checking their sample rate and importing one into a project of the other or mixing them in the same project. Ensure your sequence audio settings and your audio files specs match. And that you're working with uncompressed audio, of course.

The other main source of this kind of issue in FCP is when you've never changed the default setting (that window that pops up the first time you open with "DV NTSC 48kHz" selected) . If you've never changed that, FCP can apply a pull-up or pull-down to the audio for some reason, primarily because FCP hates audio, I think. Seriously, this issue demonstrates why you should never have a video frame rate associated with audio. It confuses people. Even the FCP coders got it wrong. I think simply having a correct Easy Setup set up solves this, but I'm not 100% on the fix. Citation Needed.

I'd wager your problem is one of the above.

IHTH

JC Boulay
Technical Director
Audio Z
Montreal, Canada
http://www.audioz.com


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Steven Probets
Re: Major Issue! Syncing video with foreign audio takes.
on Aug 10, 2011 at 1:11:26 pm

My audio settings do match that of the audio clips. They are 24-bit @ 48KHz. I know that auido is never measured in frames per second and I was quite surprised to read the 23.98fps in the file name. Therefore, the only thing I can come up with is that they were mixed at 5.1 and rendered out at 23.976 (even though my source footage with no audio is at 24p).

Do you think it would be preferable to go into Media Encoder and conform the clip to 23.976?

I am feeling I need to go back to the client and say that the audio is just not in sync and needs to be re-procesed out.

Thanks for your help!

Steven


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