Q: What custom compression setting should I use for iDVD

Well hello there, gordonpro!

Selecting and creating those custom compression settings is vital for a flawless DVD finish. Here, it's all about the space you have on the final disk. With a little trial and error, we'll be rock solid and have you finalizing that video in no time. 

Have a look at this chapter in the Compressor Manual 

Creating, Previewing, and Modifying Settings

Enjoy!