Final Cut Express Hates 12-Bit Audio

I’ve been doing a significant amount of video work lately. This led to my recent purchase of Final Cut Express (It is so wonderful having a brother-in-law who’s an Apple Store employee), and with it many changes to my typical workflow. I’m used to using Sony’s Vegas Studio product for any editing that iMovie couldn’t handle, and while FCE shares many concepts, it also looks at them from a pretty different perspective.

My most recent project involves editing a slew footage of which I was not involved in shooting. One out of five cameras that were recording during the event (a musical) was shot using 12-bit audio. This is my first experience trying to use footage with 12-bit audio in FCE, and frankly, I’m not impressed.

It is my understanding that “12-bit audio” doesn’t tell the full story – besides having a “vertical” resolution of only twelve bits, it also has a lower sample rate than 16-bit DV audio. 12-bit has a sample rate of 32,000 Hz, whereas 16-bit has a sample rate of 48,000 Hz. So far, so good.

However, when I import the 12-bit tape into FCE, I get some serious synchronization issues. After about a minute of tape, they’re noticeable – by the end of the tape, the audio and video are off by more than a second. FCE has an “Easy Setup” option for importing 32KHz DV footage – I tried this setup, as well as the normal DV setup.

After fiddling with different settings, I came across an Apple KB article about iMovie and 16-bit audio. It describes similar symptoms when exporting a Quicktime movie from iMovie. I decided to try importing the problematic tapes into iMovie, and see if I could follow the suggested instructions for “converting” the tapes to 16-bit audio. I should mention that this was using iMovie (HD) ’06.

Well, when I tried outputting the iMovie clips back to a new tape, they were being sent with only 12-bit audio, so no dice there. However, I think I found a workaround that fixes the audio sync issues.

  1. Import your DV clips using iMovie.
  2. Save your iMovie project, and then find the .iMovieProject file in the Finder. Right-click it and choose “Show Package Contents”.
  3. In the “Media” directory inside your iMovie project’s package, you should see a bunch of .dv files. FCE can work with these, but it doesn’t like to – you’ll have to render any audio before you can hear it, and playback will be SUPER-slow. To work with these files nicely in FCE, you need to convert them to Quicktime movies.
  4. Open up MPEG Streamclip (It’s free, in case you don’t already have it). If you’ve only got one DV clip that you’re working with, just drag the .dv file to the main window. If you’re working with multiple files, open up a Batch List window (Cmd+B), and drag all the .dv files into the Batch list.
  5. For your task, you want to “Export to Quicktime”, using the following settings:
    picture-3.png
  6. Note that here we’re converting the audio to 48 kHz. It may also work if you leave the sound setting at “Auto” (which will result in a file with 32 kHz sound) – this may be “truer” to the original footage, and you can leave the upsampling to FCE. YMMV.

  7. You’ll also want to check out the DV Options by clicking the “Options” button at the top right, and make sure that you’re set up for 4:3 Interlaced (or 16:9, if you’re using anamorphic 16:9 footage):
    picture-1.png
  8. Now, start the conversion process, and when it’s finished, drag the new .mov files into Final Cut, just like importing any other hard disk footage. Voila! No more sound sync problems!

I wish I knew why FCE had these issues in the first place – it seems like a rather significant oversight that projects can’t cope with these, especially since many consumer camcorders nowadays shoot with 12-bit audio by default. Oh well – in the future, I’ll try and make sure all the potential videographers for an event are consistent with 16-bit, now that I know what a pain it is to import.

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