Squeezing more onto a DVD with Final Cut/Studio Pro?

[Peter van der Linden]

I want to squeeze 2.5 hours of captured video onto a single 4.3 GB DVD.
I am willing to trade off video and audio quality for this.

I fed my original DV stream in to iMovie and captured it as 15
9-minute segments.
That is what I am trying to build and burn using DVD Studio Pro.

How can I tell what audio protocol (and hence the storage requirement)
was used?  How can I cut back on audio quality?

Before asking this question, I read and searched the 500 page
DVD Studio manual.  That suggested the bit rate could be adjusted
to reduce video storage needs.  I selected bitrate off
the Preferences menu item (of all strange places!), and tried that
with various values - 3.5, 3.1, 3.0.

In all cases, a build followed by a burn said that my 4.7GB (4.3GB
usable) DVD was not big enough, and the title bar in the DVD Studio
Pro app still displayed a 6.3GB figure.

Can anyone give me the steps to try?   I am a novice at FInal Cut and
Studio Pro, but expert otherwise.
Thanks,

Peter