I've never used the combination of iMovie and Toast for creating a DVD, but it seems that it isn't good for adjusting the compression rates. It's also very slow. It's possible that you got the error because the video and audio were too long and had not been compressed enough to fit onto a DVD. Here's a review of Toast describing its DVD bencoding capanilities:
http://www.pcpro.co.uk/macuser-reviews/46917/toast-6-titanium.html"However, behind that interface there is a wealth of new features. Perhaps most impressive amongst these are the new video tools. Toast's basic VideoCD creation capability has been beefed up and you can now create VideoCDs, Super VideoCDs and DVD movie discs with menus and buttons. The menu options are very basic, allowing you to do nothing more than define the frame of video footage from each video file to use as the button image and set chapter duration. It's no substitute for a proper DVD authoring program, but if all you want is the ability to turn QuickTime movies into a disc that can be played on your DVD player, it does the job and is very simple to use. The Universal Video Converter will convert any QuickTime-compatible video file or iMovie project to the appropriate format for the disc you're burning. Being able to drag and drop an iMovie project is useful as it precludes having to export from iMovie first, which will save you some time. The MPEG-2 encoding and multiplexing isn't fast: it took about 45 minutes to encode and burn a six minute DVD movie in our tests. Nevertheless, if you are thinking about buying a DVD burner and don't want to shell out for a dedicated authoring application, it'll do a decent job.
The other key part of the new video features is Plug and Burn. This allows you to plug a DV camera into your Mac and burn a disc directly from the footage on the camera. When it's running, Toast automatically detects a DV camera when it's plugged in. You can then rewind or play the DV tape directly from the Toast window. When you press Record, the video is captured to your hard disk. When you press stop, the captured footage is added to your Toast project."
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