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Audio Drifting Out of Sync

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Kate Flannery
Audio Drifting Out of Sync
on Sep 4, 2014 at 6:11:59 pm

Hi everyone. I'm trying to sync audio in my FCP project and for some reason the audio file is longer than the video file, which is causing them to drift out of sync when you play them together.

The audio file's audio rate is 44.1 KHz and the data rate is 39k/sec and the audio format is 32 bit Floating Point, whereas the video file's audio rate it 48KHz with data rate 23.1 MB/sec and audio format 24-bit Integer. I tried converting the audio file to conform it to the video file's specs by creating a new FCP project and dragging the audio into a new sequence with audio rate of 48KHz, rendering and exporting the sequence as an audio-to-aiff, with audio rate 48KHz, depth 24-bit, then importing into the project and everything matched but the data rate of the audio file then became 281.2k/sec, and the same problem still exists-- the audio file is still "longer" and drifts out of sync from the video file.

Any suggestions for how to solve this problem and keep the two file in sync would be much appreciated!


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John Fishback
Re: Audio Drifting Out of Sync
on Sep 11, 2014 at 5:50:24 pm

What is the frame rate of the video and where is the audio coming from? If from an outside source (i.e. a Pro Tools session) what frame rate was used in the Pro Tools session? While audio doesn't have a frame rate, DAWs may write the frame rate of the session into the header of the exported sound track. If that frame rate doesn't match your sequence frame rate, the audio will drift. Sound Devices has a free app called Wave Agent that will allow you to change the audio header to the correct frame rate.

John

MacPro 8-core 2.8GHz, 16 GB RAM, OS 10.9.4, QT10.1, Kona 3, Dual Cinema 23, ATI Radeon HD 5870, 24" TV-Logic Monitor, ATTO ExpressSAS R380 RAID Adapter, PDE enclosure with 8-drive 6TB RAID 5
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