You will want to use .mp3 or similar compressed audio format to fit more on the disc. You can use DVD as a DATA DISC (not “DVD Video”) in order to have room to fit your 40 hours of material.
Plan on the viewer using their PC to listen (or they can transfer .mp3s to an iPod or similar). You may want to use some type of “front end” interface for your presentation that will allow users to select chapters and otherwise navigate.
You might be better off selling these on a USB thumb drive. If you search online, you should be able to find some sort of “front end multimedia interface” that could be included to present the material, adding chapters and navigational features for the user.
Jeff Pulera
Safe Harbor Computers