[warnergt]

I just made my first iMovie motion video to go to DVD. It is about an hour long and you can imagine how long it takes to piece together a one hour video (not the mention the time moving files around to free up the necessary disk space).

Well, everything seemed fine util I burnt my third DVD. I was playing one to see how it looked on a TV and noticed that about half way through the audio had slipped noticeably out of sync with the video. By the end of the movie, it was terrible.

The original clips are all in sync. I had about 80 clips (not counting the added text graphics) totalling about one hour. When I exported the final movie, everything went out of whack.

Has anyone else seen this? What's the deal?

[Finrock]

I've noticed this as well, and I'll be darned if I can't figure out what is causing it. My gut feeling is that it has something to do with the transistions between clips. But still, when I play it in iMovie it is fine. Once I export it... its gets out of sync.

-Finrock

My guess as to the problem is as follows:
Exporting from iMovie to iDVD requires writing a .mov file (Quicktime 720X480 resolution, millions of colors, 16 bit audio and 29.97 fps). When iMovie is creating the file (i.e., exporting to iDVD) it is both reading the original source DV streams, audio files, etc. and writing the required .mov file. The drive in the G4 iMacs are a relatively slow 5400 rpm and evidently cannot keep up to the process of reading and writing video when exporting to iDVD. I have found that saving the original iMovie project to an external drive (even the 4500 Firefly external drive I have) eliminates the problem. Since two drives are involved, the processor can read from one and write to the other without challenging either drive. Reading from and writing to the same drive, I would venture, is the cause of your audio sync problems.

[warnergt]

When I exported the movie, I actually exported it to a second drive. I don't believe this is the problem. Exporting a movie is not a real-time process; drive speed shouldn't be a factor.

Apple has a Knowledge Base article on this issue. The problem seems to lie with recording 12 bit audio using the DV camera. 12 bit audio gradually loses sync with video in iMovie. See article at:

<a href="http://docs.info.apple.com/article.html?artnum=61636&SaveKCWindowURL=http%3A% 2F%2Fkbase.info.apple.com%2Fcgi-bin%2FWebObjects%2Fkbase.woa%2Fwa%2FSaveKCToHomePa ge&searchMode=Expert&" target="_blank">http://docs.info.apple.com/article.html?artnum=61636&SaveKCWindowURL=http%3A% 2F%2Fkbase.info.apple.com%2Fcgi-bin%2FWebObjects%2Fkbase.woa%2Fwa%2FSaveKCToHomePa ge&searchMode=Expert&</a> kbhost=kbase.info.apple.com&showButton=false&rando mValue=100&showSurvey=true&sessionID=anonymous|139 019731

[warnergt]

My camera was indeed set to 12-bit audio. I will definitely be keeping it set for 16-bit.

I still consider this problem to be a bug in Apple's software but, at least, there appears to be a workaround.

Thanks for the answer!

[warnergt]

Well, I performed the Apple recommended workaround. I transferred the files back to the camera in 16-bit audio mode. Then, I redownloaded the clips and made a DVD. The sync is definitely improved but there is still a mismatch toward the end of the one-hour video.

This truly sucks. I guess Apple doesn't expect anybody to make a DVD longer than one half hour. Does Final Cut Pro have this same bug? It is probably based on the same technology. Imagine paying $1000 and getting videos with out-of-sync audio.

Are any of your media files recorded from television, recorded from VHS tapes playing through your DV camera or mp3s from the net? These may have audio at 12 bits or lower and therefore may result in sync loss. There is also an advanced preference in iMovie that allows filtering of audio from source. Having this either on or off may result in problems depending upon the audio file source.

[warnergt]

No, all of the clips came from my camera (not counting iMovie generated titles and text). Something is funky with iMovie.

I suspect that it has something to do with the fact that the exported movie is supposed to the NTSC 29.997 fps. If it used 30 fps instead, it would be off by about 1/3 second after 1 hour. That's about what I have.

I would also consider consumer level DV cameras as potential problem sources. I have a Canon ZR30 which shoots excellent video in good light and has the option of switching from 12 to 16 bit audio. I leave it on 16 bit for the most part, but I have noticed that recording to camera from, say, a television program or VCR will switch the camera to 12 bit. Following the recorded bit from TV or VCR, the camera will default to 12 bit for recording live, until a manual change is made.

Another example of peculiar audio behavior: I created a project in iMovie, exported to camera and brought the DV tape to a video conversion shop to reformat to PAL for a European relative. The DV box used to play the tape to convert it to PAL showed the same irregular behavior that tapes with 12 bit audio do when played on this box. The technician asked if I had recorded in 12 bit audio. I said, "No," and played the tape in the camera and showed on the menu display that the tape was indeed 16 bit audio. We had to use the camera as the source for PAL conversion.

The video in that project was all live footage and the audio was a mix of live and CD background music. I wonder if overlaying 2 audio tracks in iMovie causes the camera to revert to 12 bit when exporting to it? I know that with this camera it is possible to overdub audio after the fact by using 12 bit when recording live, then inserting audio over the video. By using two audio layers in iMovie, does the camera act the same as overdubbing audio onto original video? I will have to experiment and figure that one out.