[kidtexas]

Hey all, hope you can help me out here. I made a video in iMovie. It ended up being about 30 mins long, with lots of cuts and some added audio. I imported the raw footage off of Hi8 with a Sony DV-Bridge.

Heres the deal though. I can watch the raw clip (on my harddrive) of specific scenes, and the audio matches up with the video. Same with watching it in iMovie. However, when I export the whole thing to a DV stream (so I can then encode it to various other formats) and watch that one consolidated file, audio in scenes about halfway through the video seem to have lost sync. I really only have one good section about halfway through with a good headshot of a person talking, and at that point in the video, audio seems to be lagging ever so slightly. Its not super noticeble, just a couple frames off, but after repeated watchings and examinations with the exported file and the orginal clips/viewing in imovie, it is definitely out of sync.

I am somewhat familiar with the whole 29.97 fps of NTSC, and audio sometimes being timed to 30 fps, but I seriously doubt that is the problem here, is it? I am also familiar with the idea of syncing video and audio with timing code, but the syncing on the camera is ok, the syncing in the raw imported clips is ok, and the syncing while watching in iMovie is ok. Its only after exporting the whole thing to a big file that it gets screwy. How do I fix this?

[k_munic]

have you switched WHILE doing your project from iMovie 2 to iMovie3?

have you switched WHILE doing your project from QT6.0 to QT 6.1?

lot sof users found these sync problems; reason should be some kind of "new" dv-stream coding in QT6.1. .??

no workaround known so far by me

[jcarr]

You may have been bitten by the 12-bit audio bug:

http://docs.info.apple.com/article.html?artnum=61636

[kidtexas]

No, didn't switch anything while doing the project. At a later date, I did try running the movie in iMovie3, and that made no difference - the same thing happened.

That 12 bit thing sound exactly what is going on. biatch. Thanks for the heads up.

[Josh Reid]

Hey folks...I dug up this old thread because I am having almost the same problem, but not for the same reasons.

I recorded a wedding on my Ultura using 16bit audio, did all importing & editing under iMovie 3 with the latest Quicktime installed, and can watch the movie on my iBook with no lag in sound.

However, when I tried to export the 48 minute movie back to my MiniDV Cam, at the first point where someone talks (about 6 minutes into the film, the first 6 minutes is music, so I can't tell if it's out of sync), there is a very slight lag in sound. When I first tried to export the movie, at 40 minutes the iBook export slowed to a crawl, dropping seconds worth of frames. I figured this was because I only had a few hundred MB free on my hard drive. I've since freed up approx. 3GB of space. I thought that the audio-sync issue was possibly related to this, but even with the space, I still have the audio sync issue.

So to sum up, the sound is in sync when viewing on the iBook, out of sync when I export to my camera, I'm using 16bit audio, and iMovie 3. Any suggestions as to how I can fix this?

Thanks folks!

-Josh

[warnergt]

I have the exact same problem. I believe it is a common problem. I've been wrestling with it for months. It occurs with iMovie 2 and iMovie 3. It has nothing to do with 12-bit audio.

I'll give you my theory on the problem and the (somewhat painful) workaround.

Probable explanation: Most consumer digital video cameras do not lock the audio with the video; they are clocked independently. Consequently, you obtain a number of audio samples that does not exactly match the expected number of samples for a given number of video frames. For more information on this, see:
http://www.adamwilt.com/DV-FAQ-tech.html#LockedAudio


iMovie doesn't seem to mind this sync problem when importing and playing. When exporting, however, the problem exhibits itself. Usually, the problem is not noticeable for about 10 minutes until the offset error accumulates. At 15 minutes, it is quite noticeable. At 30 minutes, it is intolerable.

Here's a (sucky) workaround:
1) Break your movie up into 5 to 10 minute clips.
2) Export the clips.
3) With the QuickTime Player, extract the audio from the clip into a separate, self-contained file (this might require QuickTime Pro -- I forget).
4) Go back to iMovie.
5) Set the sound for the original clip to 0% (turn it off).
6) Drag in the extracted sound clip for this movie clip.
7) Position audio clip and playhead at beginning of video clip.
8) From menu, select "Lock audio at playhead."
9) Do this for each clip (painful, I know).
10) Email Apple to make a real fix for this problem.

Other notes:
1) If you look at the timeline and compare the length of your video clip with the extracted audio clip, you will see that they are not the same length. This method exhibits the problem visually.
2) ALLEDGEDLY, using the QuickTime Player with QuickTime Pro, you should be able to extract the audio from a clip, remove the original audio from the movie clip, and use "Add Scaled" to write the extracted audio back while resampling it to match the video frames. I tried this. It didn't work for me. If you can get it to work, I'd like to know how.
Also, since iMovie can only import files less than 2 GB (and this method creates unusually large files), this method is pretty much restricted to files that are less than 5 minutes long.

[Josh Reid]

Thanks for the suggestions, warnergt. The odd thing with my problem was that I never had the sync issue when I worked in iMovie 2, even with projects over an hour long. Also, the sync issue in iMovie 3 happened at the beginning of the film. It didn't seem to get progressively worse.

What I did to fix it was to simply "Extract Audio From Clip" (Control-J). I could do that directly inside of iMovie, and that fixed the sync problem. I was annoyed at having to do that, as I usually put audio (music and effects) on both audio tracks and having the video's audio track seperate made things look a bit jumbled from an editing point-of-view. I was also concerned that I used to occasionally notice a tiny blip and pop at the start and finish of an extracted audio clip. However, I didn't notice this problem with this project.

I hope this is one of the (many) things that Apple addresses SOON in an iMovie update. My other complaint that is solved the same way as this one is the buzzing I get when I import footage using a Formac Studio DV.

Thanks,
Josh

[warnergt]

Thanks, Josh. You are the man. That "Extract audio" (Control-J) in iMovie may be the elegant equivalent to my inelegant fix. I'll be experimenting with that to see if it helps cure my ills.

By the way, speaking of the locked and unlocked audio, I want to convert a lot of video tapes to DVDs. My camera can digitize analog video to a digital stream. However, having to fix countless hours of out-of-sync audio would be grueling. I found this digitizer with locked audio support, the Canopus ADVC50:
http://www.cddimensions.com/dvd/cnp-advc50.asp

If you read their product data sheet, you will find it says, "Other converters can lose audio/video sync when converting analog video for longer periods of time." Sadly, that is all too true and I had to find out the hard way.

[warnergt]

Speaking of DV sound and sync, I see the just-released QuickTime 6.3 has "improvements to DV audio and video synchronization." I wonder what is different. See:
http://maccentral.macworld.com/news/.../03/quicktime/