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Audio sync drifting after conforming 25fps video to 23.98fps

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Wesley Dysart
Audio sync drifting after conforming 25fps video to 23.98fps
on Mar 2, 2015 at 11:26:13 pm

Trying to reformat a PAL 25fps master to ProRes HD at 23.98fps. I took the 25fps master file (after being uprezzed via a Teranex) and conformed it to 23.98fps. The master file is in sync all the way through the feature. No drift. The resulting HD file (after being conformed to 23.98fps) starts in sync, and stays in sync until about the last 10 minutes (97min. total running time).

I know that Cinema Tools changes the audio frequency when it conforms, so it's a little below 48khz, but it should be uniform I would think as opposed to drifting at the end. In the past I simply export from a 23.98fps/48k timeline and everything works.

This new project seems to be a bit buggy honestly. If I render out the audio at 48k and do a layback it's way off. As in, my source material doesn't line up with the export. Even though the in/out points are lined up perfectly, it shifts the audio upon rendering. Guessing that mixing 48k audio and 4,664Khz. (or something close) on the same timeline is resulting in a playback conflict.

My current thought it to simply slip the audio (below 48k on a 48k timeline) at the point that the drift occurs and spot check along the way. But it would be nice just to have a clean conversion with no drift.

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Michael Gissing
Re: Audio sync drifting after conforming 25fps video to 23.98fps
on Mar 3, 2015 at 11:10:17 pm

You could extract the audio as a wav file, drop it into a free program like Audacity and do a sample rate convert to 48 and reimport, making sure your Easy Setup frame rate matches the 23.98 sequence (another FCP Feature that causes most sync drift)

Having mixed sample rates in FCP7 is a bad idea.

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