What drove me to do the solution presented here? I tried finding comercial software for the Mac to do this and I could not find any. There are a number of comercial packages for Windows and some Open source options for Linux, however.
The solution that I found for the Mac is a combination of packages. Some are freeware (DVDBackup, Divx), some are open source (mencode, MPlayer) and some are shareware (ffmpeg GUI front end). The solution works well, but it was a lot of work to find the right software and putting all together.
How-to:
Take a DVD that you created with iMovie and iDVD and many hours of work. Extract the files from the DVD using a program called DVDBackup. This will produce a folder called VIDEO_TS containing the filesthat make up the DVD. The DVDBackup program comes with some good documentation. Make sure you read it and follow the steps.
By the way, if your computer has a DVD burner, you can burn a copy of your DVD. This is described in the DVDBackup documentation. This a much easier way to duplicate your DVDs than using iDVD. Not to mention that your iDVD project files may not be around any more, and all you have is your DVD.
Now back to our transcoding project.
In order to transcode the contents of the VIDEO_TS folder to Divx, you will need a program called ffmpeg. ffmpeg is a GUI front end for some command line utilities. The installation documentation may seem cryptic, but if you follow the steps, you will end up with a working ffmpeg. The documentation is on the website. ffmpeg web page also has instructions on how to use it to transcode. My preferred format is MPEG4[.AVI](mencoder) under the Video tab.
The other tabs (Audio, Filters, Options and Tools) may have features that you need for your partucular application of the tool. Make sure you read the documentation. Transcoding is a long process and it can take two hours or more. When it is done, you will end up with a file called movie.avi (default name that can be chagned) of size of 1.4 GB or less. You will notice that QuickTime will not play the file. You need todo one of two options:
- Get the free Divx codec for QuickTime from divx.com, and then QuickTime will be able to play movie.avi.
- Get MPlayer OS X. I find MPlayer OS X to be better than QuickTime/Divx. QuickTime with Divx is not as smooth.
It may be a quit a bit of work to get the software installed and configured properly. I can't stress it enough, read the documentation very carefully. There are many little details that are hidden in the documentation. Once every thing is installed, transcoding is a piece of cake. This was done on a 12" Powerbook with OS X 10.2.
[robg adds: A previous hint described (in less detail) another method of transcoding video.]

