Movies lose audio/video sync as they progress

One way you can save wasting discs is to create an disk image (.dmg) onto your hard disk with "File>Save as disk image" from the iDVD menu. The beauty of this is that once you've created it you can mount the image by double clicking on it in Finder. Then you can run the DVD player and it will treat the mounted dmg file as though it were a DVD in the drive. It's also a nice way to make additional copies, as you can use "Disk Utility" to burn it to disk, without the rerendering as happens in iDVD.
Have you tried splitting the clips manually into smaller chunks and seeing if that helps keep things in sync? Just move the pointer below the video display pane to a logical spot in the clip and then from iMovie menu select "Edit > split clip at playhead".

Lee -

I am also using the iMovie HD with 10.3.9 and the DAC-100 with an analog camcorder. I have the same problem with the audio sync on most DVD's. In the preview it is fine, but once it is burned, it is out more at the end of the disc. I occationally burn more than 1 hr, and allow iMovie to adjust the quality to fit it on the disc. (Don't know if this is part of the problem).

One technique I found, in a post a few months ago is to extract the audio, in iMovie (select the video track, Advanced, Extract Audio). It goes a bit quicker if you extract it before any editing of the full clip.

For me, if there is going to be a sync problem, it will appear at that time, and you can cut the track into segments and slide the audio track (select the audio track and drag with the mouse) to sync with the video. It is tedious, but does work. Once the audio is separate, iDVD will process the movie and the sync will remain where you adjusted it. I was hoping that iMovie 5.0.2 was going to correct this, but no luck.

I've got the same problem.

I also have a DAC-100, and on capture, the A/V sync is just fine. If I export the audio to it's own track, however, the audio is 5-7 seconds out of sync with the video.

The funny thing is that the audio is short. If it were due to video frame dropouts, i would think that the audio would be long, instead.

I'm continuting to check into this, to see if I can narrow things down a bit.

jf

A/V sync problems plagued iMovie and iDVD 4 but (I hope) that this was fixed in v5 so that audio extraction is no longer needed.

Another cause for A/V sync problems is if the audio is not 48 kHz. For some odd reason many camcorders default to 32 bit/32 kHz audio and it must be set at 16bit/48kHz.

iMovie 4 had/still has also a bug that very easily converted 48 kHz to 32 kHz audio behind the user's back:

http://www.sjoki.uta.fi/~shmhav/iMovie4bugs.html#32khz

One thing you can try - may not help but why not give it a go - is to open a new iMovie project and import your current project to it. Save it there and try to burn it from the new location. It may snap everything back in to sync.

John

Hi Lee -

I was not sure from your message: after extracting the audio, when you listen in iMovie, is the soud out of sync? If so, did you manually adjust the audio track to get it back in sync?

When I do this, the sync problem appears after the extract audio step. Then I can correct it by manually sliding the audio track relative to the video.

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Curtis

I've got the same problem. I've been trying to get my VHS tapes of the original Star Wars (letterbox) onto DVD. The sound and video sync perfectly in iMovie. But, when I export a Full Quality DV file, the sound is out of sync. If I don't export a movie but bring it directly into Toast with Jam, the DVD has audio out of sync. I'm using a 1.8 dual processor G5 and a data video box to bring in the signal.

I should mention that I also use the same set up to record to iMovie directly from the TV and have had no syncing problems. Also, I converted almost a hundred VHS tapes to DVD and only occcassionally have had the sync problems.

Is it some copy protection thing?

I opened my iMovie project and split the clips into chunks no longer than 10 minutes. I exported another full quality DV and when I opened it in QuickTime and previewed, the sound appears in sync. I'm going to burn a Toast DVD to see if it retains the sync.

Usually when I get the sync problem, the iMovie project is fine but the export is wacky.

And, again, this problem doesn't always occur. For example, I had brought in Wagner's Flying Dutchman with Simon Estes from VHS. The DV export was out of sync (it's kind of hard to tell when it's in German and your only guide is subtitles and lip movements). But, when I used the Toast approach, opened the package contents and use the idvd shared movie, the sync problems were gone. When I tried the same for Star Wars, the sync problems were back.

That's what makes it som frustrating. If the program would always misbehave...

I have been bitten by the sync problem as well, and have spent most of this week trying to troubleshoot it. FYI, I've been doing video conversion and editing on PC's for years, but recently moved to OSX, a Datavideo DAC-100 (Firewire DV analog capture device) and the iLife tools.

And before anyone asks, I use 16 bit audio capture. I've verified this by looking at the file that are generated. I've also looked at all the iMovie sync FAQ's on the Internet. Audio sync problems and I are old enemies. 🙂

Here's what I've found:

While the video is in it's original DV file captured by iMovie, the audio sync is perfect. I've done a 3 hour capture, and the sync was fine all the way through.

When and where the sync goes bad is when the audio is extracted from the DV file, whether by manually extracting the audio in iMovie, converting the DV to another format (including another DV file), or 'sharing' the movie to iDVD. I belive this is because the DV file format tightly links the audio to the movie timeline. When the audio is extracted, it is associated to the video only by the length (in time) of the two files. And either the audio is slightly time compressed, or the video is slightly time expanded. I suspect the audio is slightly time compressed.

I've created a predictable test case with my video, where i can capture a 15 minute block of video. At the end of the file the audio sync is perfect while in the DV format , and is ahead of the video by about 1.5 seconds after extracted.

A simple workaround would be to use a sound or video editing package that allows you chop the audio when it goes silent and to stretch the remaining audio to match the length of the video. VirtualDub and CoolEdit for the PC used to be able to do this. I've tried doing this with Quicktime Pro with no success, though. I'll keep looking for a decent OSX program to try to do this with.

This does, however, only work around the problem, not identify where it is, or fix it.

I think I've also determined that this is a problem in the standard OSX DV stream capture API, not in the conversion process of Quicktime from DV audio to whatever.

I used BTV Pro ( http://www.bensoftware.com/), a shareware/capture tool that can handle DV streams on my test case. The results were EXACTLY the same as under iMovie. I believe that BTV uses OSX's standard APIs for accessing DV streams from firewire.

Additionally, I've extracted the audio from the test DV using a non-apple DV codec (ffmpeg), and reimported it to iMovie and Quicktime. It is identical to the bad sync audio that iMovie extracts.

This leads me to believe that it's a problem with either the DAC-100's DV streams (which is set to the OSX dip switch settings) or OSX's DV capture API.

I then installed Avid Free DV ( http://www.avid.com/freedv/index.asp), a free stripped down version of a high end OSX video editing package, and successfully captured the 15 minute test case, exported it to a DV file (using both the AVID and Apple DV codecs), imported the resulting DV file into iMovie, and extracted the audio. The extracted audio synced perfectly with the video in iMovie at this point.

Just to make sure that Avid didn't just 'fix' a bad DV file, I did another test capture from iMovie, and imported the file into Avid Free DV. The resulting video had the expected sync problem, which was expected since Avid uses Quicktime for importing and exporting video.

This points the problem squarely at the Apple capture APIs, as I believe that AVID uses its own. For some reason, the files generated by iMovie/BTV exhibit the sync problems when the audio is extracted in all cases, while files generated by Avid Free DV do not.

I still don't know what the issue is with OSX/iMovie and my DAC-100. I also know that not all DAC-100 users have the problem, nor do all iMovie users with their equipment. This could be a codec incompatibility with the version of firmware on the DAC-100 with OSX, a bug in the cap

Well, ultimately Apple is going to have to fix this, if anyone does. Right now, I'm just guessing in the dark and doing black-box troubleshooting.

However, I'm pretty close to a decent, if somewhat annoying work-around. Unfortunately, it so far depends on having Quicktime Pro, and I'd prefer a free tool. I would really like to use iMovie for what I'm doing, since I have very little editing to do, the fewer times you have to touch the video the better, and the iMovie/iDVD integration is rather nice.

I'll post more when I have a How-To put together. Hint: It's very similar to the last section of http://www.danslagle.com/mac/iMovie/audio/1001.shtml

jf